Find the value of x, if

(а) 8, x, x, 50 are in proportion.

(b) 36, 90, 90, x are in proportion.

(a) Since 8, x, x, 50 are in proportion.
∴ x × x = 8 × 50
⇒ x² = 400
∴ x = 20

(b) Since 36, 90, 90, x are in proportion.
∴ 36 × x = 90 × 90
⇒ x = (90 × 90) / 36
= 225
∴ x = 225