Practice Examples for Quadratic Equation

Review :

Practice Examples 1  ,  Practice Examples 2

                                                                                     

Q.5

(5m+3)2 =4, which of the following could be the least value of m?

A.  m>0

B.  m=-1/2

C.  cannot find

D.  m=1

E.  m < – 0.5

Solution;

(5m+3)2= 4

25m2 + 30m + 9 = 4

25m2 + 30 m + 9 – 4 = 0

25m2 + 25 m + 5 m + 5=0

25m (m+1) + 5(m+1) = 0

(m+1) (25m+ 1) = 0

(m+1) = 0 or (25m +1) = 0

m = -1 or m = -1/25 = -0.04

So, least value of m = -1 which is lesser than -0.5

Hence, the correct answer is ‘E’.

                                                                                

 

Q.6

m2 – 2m – 15 = 0 and n2 – 6n + 8 = 0

Quantity A                                          Quantity B

m                                                    n

A.  If Quantity A is greater

B.  If Quantity B is greater

C.  If Quantity A and Quantity B are equal

D.  The relationship cannot be determined from given information

Solution;

Let us solve both the equation one by one.

First Equation;

m2 – 2m – 15 = 0

m2 – 5m + 3m -15 = 0

m (m – 5 ) + 3(m – 5 ) = 0

(m -5) (m + 3) = 0

(m- 5) = 0 or (m+3) = 0

m = 5 or m = -3

Second Equation;

n2 – 6n + 8 = 0

n2 – 4n – 2n + 8 = 0

n (n-4) – 2(n – 4) = 0

(n-4) ( n- 2) = 0

(n – 4) = 0 or (n – 2) = 0

n = 4 or n = 2

Now compare the two quantities.

If m = 5 than for both the values of n = 4 or n = 2 Quantity A is greater.

If m = -3 than for both the values of n = 4 or n = 2 Quantity B is greater.

Hence, we cannot arrive  any conclusion with the information given; the correct answer is ‘D’.

                                                                              

Q.7

x2  + 2x – 35  = 0, which of the following could be x , mark all such answers.

A.  x is 2 less than  7

B.  x = 0

C.  x < -1

D.  x > -8

E. -1<x<2

Solution;

x2 + 7x – 5x  -35  = 0

x(x+7) – 5(x + 7) = 0

( x + 7) ( x – 5) = 0

(x +7 ) = 0 or ( x – 5) = 0

x = -7 or x = 5

We have two solutions for the x , now we will check each answer choice

If we look at the answer choices for one of the solution of  x = 5 , ‘A’ is correct.

Choice B; x = 0 , Invalid

Choice C; x < -1 , this is right for x = -7

Choice D; x > -8, this is right for x = -7

Choice E; -1< x < 2, invalid as solutions for is lesser than-1 or greater than 2.

The correct answer is A, C and D.

Review of Quadratic Equation

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