1,
( x − 36 ) 8 − x = 3 ( x + 1 ) 3 + 12 x − 99 \left ( x-36 \right )\sqrt{8-x}= \sqrt[3]{3\left ( x+1 \right )}+12x-99 ( x − 3 6 ) 8 − x = 3 3 ( x + 1 ) + 1 2 x − 9 9
2,
2 x 16 x 2 + 3 − ( 2 x + 3 ) x 2 + 3 x + 3 = 3 − 2 x 2x\sqrt{16x^{2}+3}-\left ( 2x+3 \right )\sqrt{x^{2}+3x+3}= 3-2x 2 x 1 6 x 2 + 3 − ( 2 x + 3 ) x 2 + 3 x + 3 = 3 − 2 x
Nhân 2 vế với 2:
4 x 16 x 2 + 3 − ( 2 x + 3 ) 4 x 2 + 12 x + 12 = 6 − 4 x 4x\sqrt{16x^{2}+3}-\left ( 2x+3 \right )\sqrt{4x^{2}+12x+12}= 6-4x 4 x 1 6 x 2 + 3 − ( 2 x + 3 ) 4 x 2 + 1 2 x + 1 2 = 6 − 4 x
⟺ ( 4 x ) ( 4 x ) 2 + 3 + 2. ( 4 x ) = ( 2 x + 3 ) ( 2 x + 3 ) 2 + 3 + 2 ( 2 x + 3 ) \iff (4x)\sqrt{(4x)^2+3}+2.(4x)=(2x+3)\sqrt{(2x+3)^2+3}+2(2x+3) ⟺ ( 4 x ) ( 4 x ) 2 + 3 + 2 . ( 4 x ) = ( 2 x + 3 ) ( 2 x + 3 ) 2 + 3 + 2 ( 2 x + 3 )
Xét hàm:
f ( t ) = t t 2 + 3 + 2 t f(t)=t\sqrt{t^2+3}+2t f ( t ) = t t 2 + 3 + 2 t đồng biến
suy ra:
4 x = 2 x + 3 ⟺ x = 3 2 4x=2x+3 \iff x=\dfrac{3}{2} 4 x = 2 x + 3 ⟺ x = 2 3
3,
( 8 x + 10 ) x + 1 = ( 5 + x − 1 ) ( x + 10 x − 1 + 25 ) \left ( 8x+10 \right )\sqrt{x+1}= \left ( 5+\sqrt{x-1} \right )\left ( x+10\sqrt{x-1} +25\right ) ( 8 x + 1 0 ) x + 1 = ( 5 + x − 1 ) ( x + 1 0 x − 1 + 2 5 )
⟺ ( 2 x + 1 ) 3 + 2 x + 1 = ( 5 + x − 1 ) 3 + ( 5 + x − 1 ) \iff (2\sqrt{x+1})^3+2\sqrt{x+1}=(5+\sqrt{x-1})^3+(5+\sqrt{x-1}) ⟺ ( 2 x + 1 ) 3 + 2 x + 1 = ( 5 + x − 1 ) 3 + ( 5 + x − 1 )
Xét hàm:
f ( t ) = t 3 + t f(t)=t^3+t f ( t ) = t 3 + t đồng biến
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Last edited: 17 Tháng bảy 2019