C1:
a, Ta có:
P(-1)=3(-1)⁴-5(-1)²-2(-1)+11 = 11
Q(-1)=2(-1)⁴+(-1)³ - 2(-1)²+4(-1)-6 = -11
b, P(x)+Q(x) = (3x⁴-5x²-2x+11) + (2x⁴+x³-2x²+4x-6)
= 5x⁴+x³-7x²+2x-5
c, P(x) - Q(x)=(3x⁴-5x²-2x+11) - (2x⁴+x³-2x²+4x-6)
= x⁴ - x³ -3x² - 6x +17
C2:
A = 3/13x - 5
Để A có nghiệm thì A = 0 ⇒ 3/13x - 5 = 0
⇔ 3/13x = 5
⇔ x = 65/3
KL:........
B=x-3x²
Để B có nghiệm thì B = 0 ⇒ x - 3x² = 0
⇔ x(1-3x) = 0
⇔ \(\left[ \begin{array}{l}x=0\\1-3x=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=0\\x=1/3\end{array} \right.\)
C=x²-5x+6
Để C có nghiệm thì C=0 ⇒ x² - 5x + 6 = 0
⇔ x² -2x - 3x + 6 = 0
⇔ (x² -2x) - (3x - 6) = 0
⇔ x(x-2) - 3(x-2) = 0
⇔(x-2)(x-3) = 0
⇔\(\left[ \begin{array}{l}x-2=0\\x-3=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=2\\x=3\end{array} \right.\)
C3:
1)A=((1/7)-¹) . 1/49 .(5⁹:5⁷)
⇔ A= 7 . 1/49 . 5²
⇔A= 1/7 . 25
⇔A= 25/7
2) B= $\frac{2.6^9 - 5^5.9^4}{2^{10}.3^8+6^8.20}$
⇔B= $\frac{2^{10}.3^9-2^{10}.3^8}{2^{10}.3^8+2^{10}.3^8.5}$
⇔B=$\frac{2^{10}.3^8(3-1)}{2^{10}.3^8(1+5)}$
⇔ B = 1/3
