Respuesta :

look at the shaded right-angled triangle on the left

8 is the hypotenuse n a is opposite to the 40-degree angle

by definition, sin = opposite side / hypotenuse

so sin40=a/8

rearranging a=8sin40

Two right-angled triangles share a common side with length a.

For the inverted triangle on the left, a is the opposite side to the 40-deg angle.

Its longest side, hypotenuse, is 8cm.

Use the sine function, sin40 = opposite/hypotenuse = a/8

Multiply 8 on both sides, a = 8sin40