Expand :(9 x-5 t)(9 x+3 t) - Vidyadip

Question

Expand :$(9 x-5 t)(9 x+3 t)$

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Answer

(9x – 5t) (9x + 3t)
= (9x)² + [(-5t) + 3t] 9x + (-5t) × 3t
…[∵ (x + a) (x + b) = x² + (a + b)x + ab]
= 81x² + (-2t) × 9x – 15t²
= 81x² – 18xt – 15t²

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