If cos x = sin (20 + x) ° and 0° < x < 90°, the value of x is (What?) °.

cos (x) = sin (x + 20)

cos (x) = sin (x) cos (20) + cos (x) sin (20)

cos (x) cos (x)

1 = tan (x) cos (20) + sin (20)

cos (20) cos (20)

sec (20) = tan (x) + tan (20)

1.06 ≈ tan (x) + 0.36

- 0.36 - 0.36

0.7 = tan (x)

tan⁻¹ (0.7) = tan⁻¹[tan (x) ]

35 = x

0 < x < 90

0 < 35 < 90