Class 10 Trigonometry Practice: Choose Sides Before Ratios
Opposite and adjacent depend on the chosen angle. The hypotenuse does not: it is always opposite the right angle. Mark the angle first, name the sides second, and only then choose a trigonometric ratio.
Curriculum checked 2 October 2026 · original practice for selected skills.
Before you start
You will need: Pythagoras, fractions and square roots.
Attempt each task before opening a hint. If you need help, reveal the first hint, then the setup, then compare your written steps with the solution. Finish with the retests without referring back.
Three ideas to keep in view
For an acute angle θ in a right triangle, sin θ=opposite/hypotenuse, cos θ=adjacent/hypotenuse and tan θ=opposite/adjacent.
The identity sin²θ+cos²θ=1 involves squares. It does not say sin θ+cos θ=1.
Height-and-distance models need a clear right triangle. If eye level is above ground, include that height when the question asks for total object height.
A 5–12–13 right triangle with θ at the lower-left vertex. Relative to θ, the opposite side is 5, adjacent side 12 and hypotenuse 13. Sketch not to scale.
Try the worked example first
M10-TRIG-W1Name the sidesFocused practice
In the labelled 5–12–13 triangle, find sin θ, cos θ and tan θ for the lower-left angle.
Show your working
Need a starting hint?
The side of length 5 is opposite θ.
Still stuck? Reveal the setup
Use 13 as the hypotenuse and 12 as the adjacent side.
Show worked solution+
1
Sine and cosine
sin θ=5/13 and cos θ=12/13.
2
Tangent
tan θ=5/12; check (5/13)²+(12/13)²=1.
Answer: 5/13, 12/13 and 5/12
Before moving on: can you explain why your method works, as well as give the answer?
Your turn: three different checks
Write a method as well as an answer. The tasks change the reasoning, not just the numbers.
M10-TRIG-Q1Missing ratioFocused practice
For acute θ, sin θ=3/5. Find cos θ.
Show your working
Need a starting hint?
Use the squared identity or a 3–4–5 triangle.
Still stuck? Reveal the setup
cos²θ=1−9/25.
Show worked solution+
1
Subtract
cos²θ=16/25.
2
Choose sign
The acute-angle cosine is positive.
Answer: 4/5
Before moving on: can you explain why your method works, as well as give the answer?
M10-TRIG-Q2Exact valuesFocused practice
Evaluate 2 sin 30° + cos 60°.
Show your working
Need a starting hint?
Both trigonometric values are 1/2.
Still stuck? Reveal the setup
Substitute before adding.
Show worked solution+
1
Multiply
2 × 1/2=1.
2
Add
1+1/2=3/2.
Answer: 3/2
Before moving on: can you explain why your method works, as well as give the answer?
M10-TRIG-Q3Height modelFocused practice
From a point on level ground 10 m from a vertical pole's base, the angle of elevation to its top is 45°. Take the observation point at ground level. Find the height.
Show your working
Need a starting hint?
Height is opposite and ground distance adjacent.
Still stuck? Reveal the setup
tan45°=h/10=1.
Show worked solution+
1
Choose tangent
The hypotenuse is unnecessary.
2
Solve
h=10 m.
Answer: 10 m
Before moving on: can you explain why your method works, as well as give the answer?
Catch a likely mistake
A tempting claim: “The side that looks vertical is always opposite.”
Opposite is defined relative to the chosen angle, not the orientation of the drawing.
Close the examples and try again
These changed questions test whether you can reconstruct the method. If you use a hint, record where you got stuck and retry later. Completing this small set does not establish full chapter mastery.
M10-TRIG-R1Changed triangleIndependent retest
An acute angle has opposite side 8 and adjacent side 15 in a right triangle. Find sin θ and tan θ.
Show your working
Need a starting hint?
Find the hypotenuse first.
Still stuck? Reveal the setup
√(8²+15²)=17.
Show worked solution+
1
Hypotenuse
The square sum is 289.
2
Ratios
sin θ=8/17 and tan θ=8/15.
Answer: 8/17 and 8/15
Could you solve this without the earlier example? If not, revisit the first line where you got stuck.
M10-TRIG-R2Changed heightIndependent retest
At ground level, an observer is 12 m from a vertical pole and sees its top at 30°. Find height exactly.
Show your working
Need a starting hint?
Use tangent and keep the root exact.
Still stuck? Reveal the setup
h=12/√3.
Show worked solution+
1
Set up
tan30°=h/12.
2
Simplify
12/√3=4√3.
Answer: 4√3 m
Could you solve this without the earlier example? If not, revisit the first line where you got stuck.
Choose the next useful step
If a retest exposed the same error, rewrite the first incorrect step and explain its correction aloud. If both were independent, return to a mixed exercise or a missed paper question. A parent can ask what changed in the method rather than only asking for the answer.
Keep fractions and square roots exact unless a question asks for a decimal approximation. Rounding early can make later steps less accurate.
Can I print the questions and worked solutions separately?+
Yes. Use the two print buttons above. The question sheet leaves working space and hides solutions; the worked-solutions option includes the solution steps. Your browser can save either view as a PDF.
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