1.

If 9x2 + 25y2 = 181 and xy = - 6, find the value of 3x +5y

Answer»

Here, we will use (a+b)2 = a2 + b2 + 2ab

Given: 9x2 + 25y2 = 181 and xy = - 6

We write, (3x + 5y)2 = (3x)2 + (5y)2 + 2 x 3x x x 5y

= 181 + 30xy

= 181 + 30(- 6) = 1

(3x + 5y)2 = 1

(3x + 5y) = √1 = ±1


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