ML Aggarwal Solution Class 9 Chapter 7 Quadratic Equations MCQs

 MCQs

Choose the correct Solution from the given four options (1 to 5):

Question 1

Which of the following is not a quadratic equation :

(a) 2x2 = 3x – 5

(b) (2x- 1) (x- 1) = 2x2 – 7x + 2

(c) (2x – 1) (x + 2) = (x – 1) (x + 1)

(d) (x+ 1), = x, + 2x+2

Sol :

(2x – 1) (x – 1) = 2x2 – 7x + 2 is not a quadratic equation. 

Ans : (b)


Question 2

If 2 is a root of the quadratic equation 2x2 – kx + 1 = 0, then the value of k is

(a) 9
(b) -9
(c) $\frac{9}{2}$
(d) $-\frac{9}{2}$

Sol :

∵2 is root of 2x2-kx+1=0

∴2(2)2-k(2)+1=0

⇒8-2k+1=0=9=2k

⇒$k=\frac{9}{2}$

Ans : (c)


Question 3

If -3 is a root of the quadratic equation kx2 + 2x – 3 = 0, then the value of k is

(a) 1

(b) -1

(c) $\frac{1}{9}$

(d) $\frac{1}{-9}$

Sol :

⇒-3 is a root of quadratic equation.

⇒kx2+2x-3=0

⇒k(-3)2+2(-3)-3=0

⇒9k-6-3=0

⇒9k=9

⇒$k=\frac{9}{9}=1$

Ans (a)


Question 4

Which of the following quadratic equations has -1 as a root?

(a) x2 + 5x + 6 = 0

(b) 2x2 – 3x + 1 = 0

(c) 2x2 + x – 3 = 0

(d) 2x2 – x – 3 = 0

Sol :
∵-1 is a root of the quadratic equation.
∴It will satisfy it

⇒2x2 – x – 3 = 0

⇒2(-1)2-(-1)-3=0

⇒2+1-3=0

⇒3-3=0

Ans : (d)


Question 5

The root of the quadratic equation x2–3x–4=0 are

(a) -4, 1

(b) 4, -1

(c) 4, 1

(d) -4, -1

Sol :

⇒x2-3x-4=0

⇒x2-4x+x-4=0

⇒x(x-4)+1(x-4)

⇒(x-4)(x+1)=0

If x-4=0, then x=4

x+1=0, then x=-1

∴x=4,-1

Ans : (b)

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