Right-triangle ratios

What this lesson shows

Same triangle — 3, 4, 5. But now stand at this corner: the angle called theta. From where theta sits, every side of the triangle gets a name.

Try it yourself

Real questions from this lesson's worksheets — answers below each one.

1. Drag the point around the circle so the angle θ = 30°.
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   30
2. Right triangle: opposite = 3, hypotenuse = 5. Find sin θ
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   3/5
3. Faye writes sin θ = adjacent/hypotenuse. What's wrong?
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   sin uses the OPPOSITE side: sin θ = opposite/hypotenuse
4. Right triangle: adjacent = 4, hypotenuse = 5. Find cos θ
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   4/5