Giải:
a) \(\left(x-4\right)\left(x+4\right)-\left(1+2x\right)^2\)
\(=\left(x^2-16\right)-\left(1+4x+2x\right)\)
\(=x^2-16-1-4x-4x^2\)
\(=-17-4x-3x^2\)
Vậy ...
b) \(\left(3-2y\right)^2-\left(y-6\right)\left(y+6\right)\)
\(=9-12y+4y^2-\left(y^2-36\right)\)
\(=9-12y+4y^2-y^2+36\)
\(=45-12y+3y^2\)
Vậy ...
c) \(3x\left(x-5\right)-\left(x+7\right)\left(x-7\right)\)
\(=3x^2-15x-\left(x^2-49\right)\)
\(=3x^2-15x-x^2+49\)
\(=2x^2-15x+49\)
Vậy ...
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