maka besarnya adalah

∠C = (3x - 10)
∠D = 2x
∠C + ∠D = 90°

∠C + ∠D = 90°
3x - 10 + 2x = 90
5x - 10 = 90
5x = 90 + 10
5x = 100
x = 20°

Besar ∠C = (3x - 10)
                = 3(20) - 10
                = 60 - 10
                = 50°

semoga membantu :)

tentukan nilai x dahulu.
∠C + ∠D = 90°
3x - 10 + 2x = 90°
5x - 10 = 90°
5x = 90 + 10
5x = 100
[tex]x = \frac{100}{5} [/tex]
[tex]x = 20 [/tex]

maka, besar ∠C =
= ( 3x - 10 )°
= ( 3(20) - 10 )°
= ( 60 - 10 )°
= 50°