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Q.

If α=45+2923+45-2923, then the value of 3-21-90 _______.


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a

0

b

1

c

2

d

3 

answer is A.

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Detailed Solution


According to the problem, we are given α=45+2923+45-2923 and we need to find the value of 3-21-90 .
Let us assume α= x13+y13 such that x=45+292, y=45-292.
Let us first find the value of  3.
So, we have α=x13+y13
Let us now apply cubing on both sides.
α3=(x13+y13)3
We know that (a+b)3=a3+3a2b+3ab2+b3
α3=(x13)3+3(x13)2b+3a(y13)2+(y13)3
α3=x+3(x13y13)x13+3(x13y13) y13+y
On simplifying, we get
α3=x+3(xy)13x13+3(xy)13y13+y
Taking factor (xy)13 common, we get
α3=(x+y)+3xy13(x13+y13)....(1)
Now we will find the value of xy,
(xy)13 = ((45+292)(45-292))13
(xy)13=(2025-10352+10352-1682))13.
On Simplifying, we get
(xy)13=(343)13
As we know that,343=73
So, (xy)13 =(73)13
On solving we get
(xy)13=7 ---(2).
Let us substitute equation (2) in equation (1).
α3=(x+y)+3(7)(x13+y13)
But we already know that α=(x13+y13 such that x=45+292, y=45-292.
α3=(45+292+45-292) +21α.
On solving, we get
α3 =90+21α
α3−21α−90=0
∴ We have found the value of α3−21α−90=0 as 0.
 
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If α=45+29√23+45-29√23, then the value of ∝3-21∝-90 _______.