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C=[(x+1)(x-6)][(x-2)(x-3)]
=(x2-5x-6)(x2-5x+6)
=(x2-5x)2-36>=-36
GTNN cua C=-36 tai x2-5x=0=>x(x-5)=0=>x=0 hoac x=5
B=(x-3)2+(x-11)2
=x2-6x+9+x2-22x+121
=2x2-28x+130
=2(x2-14x+65)
=2(x2-2.7x+72-72+65)
=2[(x-7)2-49+65]
=2(x-7)2+32
=> vì 2(x-7)2 >= 0
=>2(x-7)2+32 >= 32
=> GTNN của B=32. Khi x=7
a) ta có 4p(p-a)=2(a+b+c){(a+b+c)/2}=(a+b+c)(a+b+c)=b2+2bc+c2+a2(đpcm)
1/
( a + b )3 + ( a - b )3 - 6ab2 < đã sửa >
= a3 + 3a2b + 3ab2 + b3 + a3 - 3a2b + 3ab2 - b3 - 6ab2
= 2a3
2/
A = x2 + y2 - 2x - 4y + 6 = ( x2 - 2x + 1 ) + ( y2 - 4y + 4 ) + 1 = ( x - 1 )2 + ( y - 2 )2 + 1 ≥ 1 ∀ x, y
Dấu "=" xảy ra khi x = 1 ; y = 2
=> MinA = 1 <=> x = 1 ; y = 2
B = 2x2 + 8x + 10 = 2( x2 + 4x + 4 ) + 2 = 2( x + 2 )2 + 2 ≥ 2 ∀ x
Dấu "=" xảy ra khi x = -2
=> MinB = 2 <=> x = -2
C = 25x2 + 3y2 - 10x + 11 = ( 25x2 - 10x + 1 ) + 3y2 + 10 = ( 5x - 1 )2 + 3y2 + 10 ≥ 10 ∀ x, y
Dấu "=" xảy ra khi x = 1/5 ; y = 0
=> MinC = 10 <=> x = 1/5 ; y = 0
D = ( x - 3 )2 + ( x - 11 )2
Đặt t = x - 7
D = ( t + 4 )2 + ( t - 4 )2
= t2 + 8t + 16 + t2 - 8t + 16
= t2 + 32 ≥ 32 ∀ t
Dấu "=" xảy ra khi t = 0
=> x - 7 = 0 => x = 7
=> MinD = 32 <=> x = 7
Bài 2:
a) =a2b - a2c + b2c - ab2 + ac2 - bc2
=(a2b - bc2) - (a2c - ac2) + (b2c - ab2)
=b(a-c)(a+c) - ac(a-c) - b2(a-c)
=(a - c)(ab -bc - ac - b2)
b)=(1 - 2a + a2) - (b2 - 2bc + c2)
=(1 - a)2 - (b - c)2
=(c - b - a + 1)(b - c - a + 1)
Bài 2 :
a) \(a^2-b^2-c^2+2bc=a^2-\left(b^2+c^2-bc\right)\)
\(=a^2-\left(b-c\right)^2\)
\(=\left(a-b+c\right)\left(a+b-c\right)\)
\(=\left(a+b+c-2b\right)\left(a+b+c-2c\right)\)
\(=\left(2p-2b\right)\left(2p-2c\right)\)
\(=4\left(p-b\right)\left(p-c\right)\)
b) \(p^2+\left(p-a\right)^2+\left(p-b\right)^2+\left(p-c\right)^2\)
\(=p^2+\left(p^2-2ap+a^2\right)+\left(p^2-2pb+b^2\right)+\left(p^2-2pc+c^2\right)\)
\(=4p^2+a^2+b^2+c^2-2p\left(a+b+c\right)\)
\(=a^2+b^2+c^2+4p^2-4p^2\)
\(=a^2+b^2+c^2\)
Vậy...
\(A=\left(5x\right)^2-10x+1+\left(3y\right)^2+10\)
\(=\left(5x-1\right)^2+\left(3y\right)^2+10\)
\(\Leftrightarrow Min_A=10\Leftrightarrow\hept{\begin{cases}x=\frac{1}{5}\\y=0\end{cases}}\)
\(B=\left(x+1\right)\left(x-2\right)\left(x-3\right)\left(x-6\right)\)
\(=\left[\left(x+1\right)\left(x-6\right)\right]\left[\left(x-2\right)\left(x-3\right)\right]\)
\(=\left(x^2-5x-6\right)\left(x^2-5x+6\right)\)
\(=\left(x^2-5x\right)^2-36\)
\(=\left[x^2\left(x-5\right)^2\right]-36\)
\(\Leftrightarrow Min_B=-36\Leftrightarrow\orbr{\begin{cases}x=0\\x=5\end{cases}}\)
Vậy ...