a) \(\left(x-5\right)\left(x+2\right)+\left(x+1\right)\left(2-x\right)=15\)
\(\Leftrightarrow x^2+2x-5x-10+2x-x^2+2-x=15\)
\(\Leftrightarrow-2x-8=15\)
\(\Leftrightarrow-2x=23\)
\(\Leftrightarrow x=-\frac{23}{2}\)
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b) \(\left(2x-3\right)\left(x+5\right)-\left(x-2\right)\left(2x+1\right)=3\)
\(\Leftrightarrow2x^2+10x-3x-15-2x^2-x+4x+2=3\)
\(\Leftrightarrow10x-13=3\)
\(\Leftrightarrow10x=16\)
\(\Leftrightarrow x=\frac{8}{5}\)
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