Solving Equation 5

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Solve : √(9x + 81) = x + 5

Solution: √(9x + 81) = x + 5

=> 9x + 81 = (x+5)² [ Squaring both side ]

=> 9x + 81 = x² + 10x + 25

=> x² + x - 56 = 0

=> x² +8x - 7x - 56 = 0

=> x( x + 8) - 7(x +8) = 0

=> (x-7)(x+8) = 0

so, either x-7 = 0

=> x=7

or, x+8 = 0

=> x=-8

So, x= {7,-8}.