Aptitude - Square Root and Cube Root - Discussion

Discussion Forum : Square Root and Cube Root - General Questions (Q.No. 6)
6.

If a = 0.1039, then the value of 4a2 - 4a + 1 + 3a is:

0.1039
0.2078
1.1039
2.1039
Explanation:

4a2 - 4a + 1 + 3a = (1)2 + (2a)2 - 2 x 1 x 2a + 3a

= (1 - 2a)2 + 3a

= (1 - 2a) + 3a

= (1 + a)

= (1 + 0.1039)

= 1.1039

Discussion:
70 comments Page 1 of 7.

How we get the formula. I can't understand, give me the clarification about it.

Formula: a2 + b2 - 2ab = (a - b)2

But I get (a-1/2) using (-b + -sqrt (b2 - 4ac) /2a).

In this case ans. Can also proceed with (2a - 1)^2 ??? Plz clarify !!

Sorry you are wrong
4*a*a - 4*a + 1 can be written as
4*a*a - 2*a -2*a +1

Taking 2*a common
2*a(2*a-1) -(2*a - 1)

Hence (2*a-1)(2*a-1) but it is given as (1-2*a)(1-2*a) is completely wrong how can he get that ????

If im wrong please explain me ???

The formula => a2 + b2 - 2ab = (a - b)2 can be
a2 + b2 - 2ab = (b - a)2 as well. so we can get it as (2a - 1) +3a . Then the answer will be different.

FOMULA (a-b) 2 is ok. But how square has gone from (1-2a) 2 and it written as (1-2a) +3a.

Square root(a*a)=a
similarly square root{(1-2a)*(1-2a)}=1-2a
but my doubts is that why can't be (2a-1)

Can any one help with this problem ?

Yes, Mariapan,
I agree with you.
Why it's not (2a-1)?