\(2a^2+2b^2=5ab\)
\(=>2a^2+2b^2-5ab=0\)
\(=>2a^2-5ab+2b^2=0\)
\(=>2a^2-4ab-ab+2b^2=0\)
\(=>2a\left(a-2b\right)-b\left(a-2b\right)=0=>\left(2a-b\right)\left(a-2b\right)=0\)
=>2a-b=0 hoặc a-2b=0
=>2a=b hoặc a=2b
=>a=b/2 hoặc a=2b
Vì b>a(theo đề)
=>a=2b là vô lí
do đó a=b/2
Thay a=b/2 vào M ta có:
\(M=\frac{a-b}{a+b}=\frac{\frac{b}{2}-b}{\frac{b}{2}+b}=\frac{\frac{b-2b}{2}}{\frac{b+2b}{2}}=\frac{-\frac{b}{2}}{\frac{3b}{2}}=\frac{-b}{3b}=-\frac{1}{3}\)
Vậy M=-1/3
câu 5:
\(2a^2+2b^2=5ab\)
\(=>2a^2+2b^2-5ab=0=>2a^2-5ab+2b^2=0\)
\(=>2\left(a^2-\frac{5}{2}ab+b^2\right)=0\)
\(=>a^2-\frac{5}{2}ab+b^2=0\)
\(=>a^2-\frac{5}{4}ab-\frac{5}{4}ab+\frac{25}{4}b^2-\frac{21}{4}b^2=0\)
\(=>a\left(a-\frac{5}{4}b\right)-\frac{5}{4}b\left(a-\frac{5}{4}b\right)-\frac{21}{4}b^2=0\)
\(=>\left(a-\frac{5}{4}b\right)^2-\frac{21}{4}b^2=0\)
\(\)
F(x) có nghiệm
<=>F(x)=0
<=.2x+5=0<=>2x=-5<=>x=-5/2
Vậy x=-5/2 là nghiệm của F(x)
G(x) có nghiệm <=> G(x)=0
<=>2x2-18=0
<=>2x2=18<=>x2=9<=>x=-3;x=3
Vậy x=-3;x=3 là nghiệm của G(x)
a, F(x)=2x+5
2x+5=0
2x =0-5
2x =-5
x =-5:2
x =-2,5
b,G(x)=2x2-18
2x2-18=0
2x2 =0-18
2x2 = -18
x2 =-18:2
x2 =-9
=>x =+3
Câu 1 :
A=(\(-\frac{3}{7}\)x2yz)(\(\frac{14}{9}\)y3z)(-3x2)2
=\(-\frac{3}{7}x^2yz.\frac{14}{9}y^3z.-3x^4\)
=\(-\frac{3}{7}.\frac{14}{9}.\left(-9\right).x^2.x^4.y.y^3.z.z\)
\(6x^6y^4z^2\)
Câu 2 :a,
\(B\left(x\right)=x^3-3x^2+2x+\frac{7}{2}\)
Thay B(2) vào đa thức :\(2^3-3.2^2+2.2+\frac{7}{2}\)
\(=6-3.4+2.2+\frac{7}{2}\)
\(=6-12+4+\frac{7}{2}\)
\(=\frac{3}{2}\)
b,
\(C\left(x\right)=2x^4+x^3-x+3x^2+5x-2x^4-\frac{9}{2}\)
\(=2x^4+x^3-x+3x^2+5x-2x^4-\frac{9}{2}\)
\(=2x^4-2x^4+x^3-x+5x+3x^2-\frac{9}{2}\)
\(=x^3+4x+3x^2-\frac{9}{2}\)
\(=x^3+3x^2+4x-\frac{9}{2}\)
c,D(x)=B(x)+C(x)
\(=x^3-3x^2+2x+\frac{7}{2}+x^3+3x^2+4x-\frac{9}{2}\)
\(=x^3+x^3-3x^2+3x^2+2x+4x+\frac{7}{2}-\frac{9}{2}\)
\(=2x^3+6x-1\)
E(x)=B(x)-C(x)
\(=\left(x^3-3x^2+2x+\frac{7}{2}\right)-\left(x^3+3x^2+4x-\frac{9}{2}\right)\)
\(=x^3-3x^2+2x+\frac{7}{2}-x^3-3x^2-4x+\frac{9}{2}\)
\(=x^3-x^3-3x^2-3x^2+2x-4x+\frac{7}{2}+\frac{9}{2}\)
\(=-6x^2-2x+8\)
cho g(x)= \(2x^2-18=0\)
\(=>2x^2=18\)
\(=>x^2=9=>x=3\)hoặc x=-3
bư
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