ae giúp mình với ạ
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a.
\(A\left(x\right)+B\left(x\right)+C\left(x\right)=\left(3x^6-5x^4+2x^2-7\right)+\left(8x^6+7x^4-x^2+11\right)+\left(x^6+7x^4-x^2+6\right)\)
\(=12x^6+9x^4+10\)
b.
\(A\left(x\right)-B\left(x\right)+C\left(x\right)=\left(3x^6-5x^4+2x^2-7\right)-\left(8x^6+7x^4-x^2+11\right)+\left(x^6+7x^4-x^2+6\right)\)
\(=-4x^6-5x^4+2x^2-12\)
c.
\(A\left(x\right)-B\left(x\right)-C\left(x\right)=\left(3x^6-5x^4+2x^2-7\right)-\left(8x^6+7x^4-x^2+11\right)-\left(x^6+7x^4-x^2+6\right)\)
\(=-6x^6-19x^4+4x^2-24\)
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Do \(f\left(1\right)=g\left(2\right)\) nên:
\(2.1^2+a.1+4=2^3-5.2-b\)
\(\Rightarrow a+6=-2-b\)
\(\Rightarrow a=-b-8\) (1)
Do \(f\left(-1\right)=g\left(5\right)\) nên:
\(2.\left(-1\right)^2+a.\left(-1\right)+4=5^3-5.5-b\)
\(\Rightarrow-a+6=100-b\)
\(\Rightarrow a=b-94\) (2)
(1);(2) \(\Rightarrow-b-8=b-94\)
\(\Rightarrow2b=94-8\)
\(\Rightarrow b=43\)
\(\Rightarrow a=43-94=-51\)
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9a.
Do \(P\left(-2\right)=7\)
\(\Rightarrow a.\left(-2\right)+5=7\)
\(\Rightarrow-2a=2\)
\(\Rightarrow a=-1\)
b.
Do \(P\left(0\right)=-2\)
\(\Rightarrow a.0+b=-2\)
\(\Rightarrow b=-2\)
Do \(P\left(-3\right)=-1\)
\(\Rightarrow a.\left(-3\right)+b=-1\)
\(\Rightarrow-3a-2=-1\)
\(\Rightarrow-3a=1\)
\(\Rightarrow a=-\dfrac{1}{3}\)
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- Kẻ EF,CH lần lượt vuông góc với AB (F,H thuộc AB).
- Ta có: EF,CH lần lượt vuông góc với AB (gt)
=>EF//CH.
- Xét tam giác ACH có:
EF//CH (cmt)
=>\(\dfrac{EF}{CH}=\dfrac{AE}{AC}=\dfrac{1}{4}\) (định lí Ta-let)
- \(\dfrac{S_{ABC}}{S_{ADE}}=\dfrac{CH}{EF}.\dfrac{AB}{AD}=4.3=12\)(cm2)
=>SADE=\(\dfrac{1}{12}S_{ABC}=\dfrac{1}{12}.60\)=5 (cm2)
* SDBEC=SABC-SADE=60-5=55(cm2)
cảm ơn bạn nhé!!!!!