[tex]\displaystyle\bf\\(8x-7y)^{2} -(70x^{2}+45y^{2} )-(-15x^{2} +48xy)=\\\\=(8x)^{2} -2\cdot 8x\cdot 7y+(7y)^{2} -70x^{2} -45y^{2}+15x^{2} -48xy=\\\\=64x^{2} -112xy+49y^{2} -70x^{2} -45y^{2}+15x^{2} -48xy=\\\\=\underbrace{(64x^{2} -70x^{2} +15x^{2} )}_{9x^{2} }-\underbrace{(112xy+48xy)}_{160xy}+\underbrace{(49y^{2}-45y^{2} )}_{4y^{2}} =\\\\=9x^{2} -160xy+4y^{2}[/tex]
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[tex]\displaystyle\bf\\(8x-7y)^{2} -(70x^{2}+45y^{2} )-(-15x^{2} +48xy)=\\\\=(8x)^{2} -2\cdot 8x\cdot 7y+(7y)^{2} -70x^{2} -45y^{2}+15x^{2} -48xy=\\\\=64x^{2} -112xy+49y^{2} -70x^{2} -45y^{2}+15x^{2} -48xy=\\\\=\underbrace{(64x^{2} -70x^{2} +15x^{2} )}_{9x^{2} }-\underbrace{(112xy+48xy)}_{160xy}+\underbrace{(49y^{2}-45y^{2} )}_{4y^{2}} =\\\\=9x^{2} -160xy+4y^{2}[/tex]