Papy

Exact Trigonometric Values - Edexcel GCSE Higher Maths

Typically 1-4 marks per paper, concentrated on Paper 1 · Spec 1MA1

Spec reference G21 on Edexcel's 1MA1 is a memory list and nothing else: the exact values of sinθ\sin \theta and cosθ\cos \theta at 00^\circ, 3030^\circ, 4545^\circ, 6060^\circ and 9090^\circ, together with the exact value of tanθ\tan \theta at 00^\circ, 3030^\circ, 4545^\circ and 6060^\circ. Tangent stops at 6060^\circ because tan90\tan 90^\circ has no value. G21 is Higher tier only, so a Foundation candidate never meets it, and it is the one part of the trigonometry content that cannot be looked up during the exam.

That last point is the whole reason this topic exists as a separate page. The Exam Aid issued with every 1MA1 paper for the 2025 to 2027 windows prints the three right-angled ratios, the sine rule, the cosine rule and Area=12absinC\text{Area} = \frac{1}{2}ab\sin C. It does not print a single numerical value, so a question that hands you sin60\sin 60^\circ to work with hands you nothing you can read off the insert. Edexcel asks for it in three shapes: a one-mark 'write down the exact value of cos30\cos 30^\circ' near the front of Paper 1, a two- or three-mark combination such as 10cos30+3tan3010\cos 30^\circ + 3\tan 30^\circ to be written in the form aba\sqrt{b}, and a triangle whose angle happens to be 30, 45 or 60 degrees where the answer must be left as a surd. The values also turn up on Papers 2 and 3, because the word 'exact' in a stem overrules the calculator sitting on the desk.

Almost every dropped mark here is one of two things. The first is writing sin60=12\sin 60^\circ = \frac{1}{2}, which is the value of sin30\sin 30^\circ; the pair get swapped more than any other. The second is converting a correct surd into 0.866 and putting that on the answer line, which loses the accuracy mark on a question that asked for an exact value. The fix for both is the same and takes under a minute at the start of the paper: sketch half an equilateral triangle of side 2 and an isosceles right-angled triangle with two sides of 1, label them, and read every value you need off your own sketches rather than out of memory under pressure.

Worked example

Triangle ABC has a right angle at B. Angle BAC = 6060^\circ and AB = 6 cm. Do not use a calculator. Work out the exact perimeter of triangle ABC. Give your answer in the form a+b3a + b\sqrt{3} cm, where aa and bb are integers.
[4 marks]
  1. AB is next to the 6060^\circ angle and BC faces it, so BC is the opposite and AB the adjacent: tan60=BC6\tan 60^\circ = \frac{BC}{6}. Since tan60=3\tan 60^\circ = \sqrt{3}, BC=63BC = 6\sqrt{3} cm.
    M1: tan chosen for opposite over adjacent, with tan60\tan 60^\circ recalled as 3\sqrt{3}
  2. AC faces the right angle, so it is the hypotenuse: cos60=6AC\cos 60^\circ = \frac{6}{AC}. Since cos60=12\cos 60^\circ = \frac{1}{2}, AC=6÷12=12AC = 6 \div \frac{1}{2} = 12 cm.
    M1: dividing by the half rather than multiplying by it, so AC comes out as 12 and not 3
  3. Perimeter =AB+BC+AC=6+63+12= AB + BC + AC = 6 + 6\sqrt{3} + 12.
    M1: all three sides added, the surd term left alone
  4. Collect the two integers: perimeter =18+63= 18 + 6\sqrt{3} cm, so a=18a = 18 and b=6b = 6.
    A1: 18+6318 + 6\sqrt{3}; do not turn it into 28.4, the question said exact

Practice questions

These are original questions in Edexcel 1MA1 Higher style, and all of them are meant to be done with the calculator face down. Where an answer is a surd you are asked for the integers inside it, or given four forms to choose between, because a square root sign cannot be typed into a box. Every triangle is described in words, so sketch it and mark the right angle before you pick a ratio.

No account needed: the questions below are always free to check, plus 8 extra questions today. Your score so far updates as you go.

  1. Question 1 Warm-up [1 mark]
    Write down the exact value of tan 30 degrees.
    Answer options for question 1
  2. Question 2 Warm-up [2 marks]
    Triangle PQR has a right angle at Q. PQ = 6 cm and QR = 6 cm. Work out the size of angle QPR, in degrees.
  3. Question 3 Exam pace [2 marks]
    Which of these is equal to 13\frac{1}{\sqrt{3}}?
    Answer options for question 3
  4. Question 4 Exam pace [2 marks]
    xx is an acute angle and tanx=3\tan x = \sqrt{3}. Work out the value of xx, in degrees.
  5. Question 5 Stretch [3 marks]
    The diagonal of a square is 8 cm long. The length of a side of the square can be written as aba\sqrt{b} cm, where aa and bb are integers and bb is as small as possible. Write down the value of aa and the value of bb.
  6. Question 6 Stretch [5 marks]
    PS is perpendicular to the straight line SR, and PS = 6 cm. Q is a point on SR between S and R. Angle SPQ = 30 degrees and angle SPR = 60 degrees. The length of QR can be written as aba\sqrt{b} cm, where aa and bb are integers and bb is as small as possible. Write down the value of aa and the value of bb.

Common mistakes examiners see

  • Swapping the 30 and 60 degree pair, writing sin60=12\sin 60^\circ = \frac{1}{2} or cos30=12\cos 30^\circ = \frac{1}{2}. In an area calculation that single slip turns 12312\sqrt{3} into 12.

    Anchor them to the half-equilateral triangle with sides 1, 3\sqrt{3} and 2. The short side of 1 faces the 3030^\circ angle, so the 12\frac{1}{2} belongs to sin30\sin 30^\circ and to cos60\cos 60^\circ. Sketch that triangle in the margin before you start rather than trusting recall.

  • Replacing the surd with a decimal: giving cos30\cos 30^\circ as 0.866 or an area of 12312\sqrt{3} as 20.8 when the question says 'exact' or 'in the form aba\sqrt{b}'.

    The word exact in an Edexcel stem means no rounding anywhere, so the answer line has to carry a fraction or a surd. Rounding costs the accuracy mark even when every earlier line is right.

  • Expecting the values on the Exam Aid and hunting for them mid-question, or worse, guessing because the insert only shows sinA=ac\sin A = \frac{a}{c}.

    The insert gives the ratios, the sine and cosine rules and 12absinC\frac{1}{2}ab\sin C, and no numbers at all. Write out the nine values at 30, 45 and 60 degrees on the front of the paper in the first minute, while nothing else is competing for your attention.

  • Multiplying by the fraction instead of dividing by it: from sin30=4x\sin 30^\circ = \frac{4}{x} writing x=4×12=2x = 4 \times \frac{1}{2} = 2 rather than x=4÷12=8x = 4 \div \frac{1}{2} = 8.

    When the unknown sits underneath, it changes places with the trig value. Then size-check: xx here is a hypotenuse, so it cannot come out shorter than the 4 cm side.

  • Losing a factor of a half in the area formula, so 12×8×10×sin60\frac{1}{2} \times 8 \times 10 \times \sin 60^\circ is written as 40340\sqrt{3} instead of 20320\sqrt{3}.

    There are two halves in play, the one in the formula and the one inside 32\frac{\sqrt{3}}{2}. Work out 12×8×10=40\frac{1}{2} \times 8 \times 10 = 40 on its own line first, then multiply by 32\frac{\sqrt{3}}{2} to get 20320\sqrt{3}.

Frequently asked questions

Are exact trig values on the Edexcel formulae sheet?
No, and that is the trap. The Higher Exam Aid issued with each 1MA1 paper carries the three right-angled ratios, the sine rule, the cosine rule and the area formula 12absinC\frac{1}{2}ab\sin C, but it prints no numerical values. sin30\sin 30^\circ, cos45\cos 45^\circ and the rest are still straight recall, which is why a question can ask for them for one mark.
Which exact trigonometric values do I have to learn for Edexcel Higher?
Spec reference G21 asks for sinθ\sin \theta and cosθ\cos \theta at 0, 30, 45, 60 and 90 degrees, and tanθ\tan \theta at 0, 30, 45 and 60 degrees. That is fourteen values in total. tan90\tan 90^\circ is not on the list because it has no value: the adjacent side has shrunk to zero and a calculator returns an error.
Are exact trig values on the Foundation paper?
No. G21 is Higher tier only, so Foundation candidates are never asked for them, even though they meet the same three ratios under G20. It is one of the shorter Higher-only spec points, which makes it worth learning properly: a mark for writing down tan60=3\tan 60^\circ = \sqrt{3} is as good as any other mark on the paper.
What is the easiest way to remember the exact trig values?
Draw the two triangles instead of memorising a table. An equilateral triangle of side 2 cut down the middle gives a right-angled triangle with sides 1, 3\sqrt{3} and 2, which produces every value at 30 and 60 degrees. A square of side 1 cut along its diagonal gives sides 1, 1 and 2\sqrt{2}, which produces the 45 degree values. The 0 and 90 degree values come from imagining the triangle flattened or stood upright.