Question

2.47. Найдите значение выражения: 4,6x²y-2, 2xy+7y² -(7,8xy – 3,4х²у +7у²) при: 1) x=2, y=5; 2) x=-2, y=3.
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Answer 1

1)4,6x²y-2,2xy+7y²-(7,8xy–3,4х²у+7у²)=4,6×2²×5-2,2×2×5+7×5²-(7,8×2×5-3,4×2²×5+7×5²)=4,6×2²×5-2,2×2×5+7×5²-5(7,8×2-3,4×2²+7×5)=4,6×2²×5-2,2×2×5(15,6-3,4×4+35)=4,6×2²×5-2,2×2×5+7×5²-5(15,6-13,6+35)=4,6×2²×5-2,2×2×5+7×5²-5×37=5(4,6×2²-2,2×2+7×5-37)=5(4,6×4-4,4+35-37=5(18,4-4,4+35-37=5×12=60

2)4,6x²y-2,2xy+7y²-(7,8xy–3,4х²у+7у²)=4,6×(-2)²×3-2,2×(-2)×3+7×3²-(7,8×(-2)×3-3,4×(-2)²×3+7×3²)=4,6×(-2)²×3+2,2×2×3+7×3²-(-7,8×2×3-3,4×(-2)²×3+7×3²)=4,6×(-2)²×3+2,2×2×3+7×3²-3(-7,8×2-3,4×(-2)²+7×3)=4,6×(-2)²×3+2,2×2×3+7×3²-3(-15,6-3,4×2²+21)=4,6×2(-2)²×3+2,2×2×3+7×3²-3(-15,6-3,4×4+21)=4,6×(-2)²×3+2,2×2×3+7×3²-3(-15,6-13,6+21)=4,6×(-2)²×3+2,2×2×3+7×3²-3×(-8,2)=4,6×(-2)²×3+2,2×2×3+7×3²+3×8,2=3(4,6×(-2)²+2,2×2+7×3+8,2)=3(4,6×2²+4,4+21+8,2)=3(4,6×4+4,6+21+8,2)=3(18,4+4,4+21+8,2)=3×52=156