Question

What is this equation called and how do I do it?

Answer 1

DE ≈ 40

Explanation:

Using the Sine rule in Δ DEF

∠ D = 180° - (58 + 87)° ← sum of angles in a triangle

∠ D = 180° - 145° = 35° , then

`(DE)/(sin87)` =
`(EF)/(sin35)` =
`(23)/(sin35)` ( cross- multiply )

DE × sin35° = 23 × sin87° ( divide both sides by sin35° )

DE =
`(23sin87)/(sin35)` ≈ 40 units ( to the nearest whole number )