\(49.\left(y-4\right)^2-9y^2-36y-36\)
\(=7^2\left(y-4\right)^2-\left(9y^2+36y+36\right)\)
\(=\left(7y-28\right)^2-\left(3y+6\right)^2\)
\(=\left(7y-28+3y+6\right).\left(7y-28-3y-6\right)\)
\(=\left(10y-22\right).\left(4y-34\right)\)
\(=4.\left(5y-11\right).\left(2y-17\right)\)
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\(49\left(y-4\right)^2-9y^2-36y-36\)
\(=\) \(4\left(2y-17\right)\left(5y-11\right)\)
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