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Learn Geometry and Trigonometry Right-triangle trigonometry

Find missing sides

Pick the ratio that links what you know to what you want.

Geometry and Trigonometry: Right-triangle trigonometry

Label the sides from the angle.
Choose sine, cosine or tangent.
Write the equation and solve.

Work through it

Angle $3 0^{\circ}$ , hypotenuse 10. Find the opposite side.

$sin 3 0^{\circ} = \frac{x}{10}$

$x = 10 (0.5) = 5$

Angle $4 5^{\circ}$ , adjacent 7. Find the opposite side.

$tan 4 5^{\circ} = \frac{x}{7}$

$x = 7$

Watch out for this

Calculator in radians.

Check that it's in degree mode when the angles are in degrees.

Your turn

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