Toán Lớp 8: Rút gọn:
$(x+5)(x^{2}- 5x+25)- x^{2}(x-5)$
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Toán Lớp 8: Rút gọn:
$(x+5)(x^{2}- 5x+25)- x^{2}(x-5)$
Comments ( 2 )
=(x+5)(x^2-x.5+5^2)-x^2.(x-5)
=x^3+5^3-(x^3-5x^2)
=x^3+125-x^3+5x^2
=(x^3-x^3)+125+5x^2
=125+5x^2
Áp dụng hằng đẳng thức:
A^3+B^3=(A+B)(A^2-AB+B^2)