1. Tìm x:
a. 5x(x-3)(x+3)-(2x-3)^2-5(x+2)^3+34x (x+2)=0
b. (x-2)^3+6(x+1)^2-(x-3) (x^2+3x+9)=97
2. Tính:
A=35^3+13^3 trên48 -35×13
B=68^3-52^3 trên16 +68×52
Giúp mk với ạ
Mk đang cần gấp lắm
1. Tìm x:
a. 5x(x-3)(x+3)-(2x-3)^2-5(x+2)^3+34x (x+2)=0
b. (x-2)^3+6(x+1)^2-(x-3) (x^2+3x+9)=97
2. Tính:
A=35^3+13^3 trên48 -35×13
B=68^3-52^3 trên16 +68×52
Giúp mk với ạ
Mk đang cần gấp lắm
Đáp án:
$\begin{array}{l}
1)a)5x\left( {x – 3} \right)\left( {x + 3} \right)\\
– {\left( {2x – 3} \right)^2} – 5{\left( {x + 2} \right)^3} + 34x\left( {x + 2} \right) = 0\\
\Rightarrow 5x\left( {{x^2} – 9} \right) – \left( {4{x^2} – 12x + 9} \right)\\
– 5\left( {{x^3} + 6{x^2} + 12x + 8} \right) + 34{x^2} + 68x = 0\\
\Rightarrow 5{x^3} – 45x – 4{x^2} + 12x – 9\\
– 5{x^3} – 30{x^2} – 60x – 40 + 34{x^2} + 68x = 0\\
\Rightarrow – 25x – 49 = 0\\
\Rightarrow x = \dfrac{{ – 49}}{{25}}\\
b){\left( {x – 2} \right)^3} + 6{\left( {x + 1} \right)^2} – \left( {x – 3} \right)\left( {{x^2} + 3x + 9} \right) = 97\\
\Rightarrow {x^3} – 6{x^2} + 12x – 8 + \\
6{x^2} + 12x + 6 – \left( {{x^3} – 27} \right) = 97\\
\Rightarrow {x^3} + 24x – 2 – {x^3} + 27 = 97\\
\Rightarrow 24x = 72\\
\Rightarrow x = 3\\
B2)\\
A = \dfrac{{{{35}^3} + {{13}^3}}}{{48}} – 35.13\\
= \dfrac{{\left( {35 + 13} \right)\left( {{{35}^2} – 35.13 + {{13}^2}} \right)}}{{48}} – 35.13\\
= \dfrac{{48.\left( {{{35}^2} – 35.13 + {{13}^2}} \right)}}{{48}} – 35.13\\
= {35^2} – 2.35.13 + {13^2}\\
= {\left( {35 – 13} \right)^2}\\
= {\left( {22} \right)^2}\\
= 484\\
B = \dfrac{{{{68}^3} – {{52}^3}}}{{16}} + 68.52\\
= \dfrac{{\left( {68 – 52} \right)\left( {{{68}^2} + 68.52 + {{52}^2}} \right)}}{{16}} + 68.52\\
= {68^2} + 2.68.52 + {52^2}\\
= {\left( {68 + 52} \right)^2}\\
= {120^2}\\
= 14400
\end{array}$