37: \(\left(x-1\right)^2-\left(x-3\right)^2\)
\(=\left(x-1-x+3\right)\left(x-1+x-3\right)\)
\(=2\left(2x-4\right)=4x-8\)
38: \(\left(2x-1\right)^2-\left(x+3\right)^2\)
\(=4x^2-4x+1-x^2-6x-9\)
\(=3x^2-10x-8\)
39: \(\left(x-1\right)^2-\left(2x-3\right)^2\)
\(=x^2-2x+1-\left(4x^2-12x+9\right)\)
\(=x^2-2x+1-4x^2+12x-9\)
\(=-3x^2+10x-8\)
40: \(\left(2x+1\right)^2-\left(x-2\right)^2\)
\(=4x^2+4x+1-\left(x^2-4x+4\right)\)
\(=4x^2+4x+1-x^2+4x-4\)
\(=3x^2+8x-3\)
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