1.

Find the following products : (2x - 3) (2x - 5)

Answer»

Using the identity : (x + a) (x + b) = x2 + (a + b) x + ab, we have 

(2x - 3) (2x + 5) = (y - 3) (y + 5), where y = 2x 

 = {y + (-3)} (y + 5) 

 = y2 + {(-3) + 5} y + (-3) × 5 

 = y2 + 2y - 15 

 = (2x)2 + 2 × 2x - 15 

 = 4x2 + 4x - 15



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