6x-y=13
4x+5y=3
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y=6x-13
4x+5y=3
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y=6x-13
4x+5(6x-13)=3
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y=6x-13
4x+30x-65=3
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y=6x-13
34x=68, x=68/34, x=2
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y=6.2-13=12-13=-1, y=-1
x=2
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/x,y/=/2,-1/
См скриншот
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1+sin(π+α)*cos(3π/2+α)=1+(-sin(α))*sin(α)=1-sin²α=cos²α