Toán Lớp 8: Đơn giản các biểu thức:
a) (3b^2)^2 – b^3(1- 5b);
b) y(16y – 2y^3) – (2y^2)^2;
c) (-1/2x)^3 – x(1 – 2x – 1/8x^2);
d) (0,2a^3)^2 – 0,01a^4 (4a^2 – 100).
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Toán Lớp 8: Đơn giản các biểu thức:
a) (3b^2)^2 – b^3(1- 5b);
b) y(16y – 2y^3) – (2y^2)^2;
c) (-1/2x)^3 – x(1 – 2x – 1/8x^2);
d) (0,2a^3)^2 – 0,01a^4 (4a^2 – 100).
Comments ( 1 )
= 9b^4 – b^3.(1 – 5b)
= b^3.(9b) – b^3.(1 – 5b)
= b^3.(9b – 1 + 5b)
= b^3.(14b – 1)
= 14b^4 – b^3
= y(16y – 2y^3) – 4y^4
= y.y.(16 – 2y^2) – y^2.(4y^2)
= y^2.(16 – 2y^2) – y^2.(4y^2)
= y^2.(16 – 2y^2 – 4y^2)
= y^2.(16 – 6y^2)
= 16y^2 – 6y^4