( x 2 − 7 x + 1 1 ) x 2 − 6 x − 7 = 1
Find the sum of the values of x that satisfy the above equation.
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Justin Wong I got this wrong today because I forgot the base = − 1 case. Did you?
Hey same here!!
same here buddy..
yea i got that wrong becuz of that
I didn't notice that this is Level 5. Thought too much about others. Initially thought that the figures are total number of roots. Too happy to find 4 of 13.
Yeah, the same thing.
Ohh !!same here I too missed the 3rd case ...
Same I missed the 3rd.
in case 1, we could use vieta's to determine the sum
Nice. I thought this would be a lot harder.
Shouldn't x ≡ 1 ( m o d 2 )
the question should mention 'real' because x 2 − 7 x + 1 1 = e x p ( n 2 k π i ) x 2 − 6 x − 7 = z n for some integer k,z and n, than the expression would be 1
Overrated!
The condition of the problem is satisfied if one of the following cases hold true: Case 1 : x 2 − 7 x + 1 1 = 1 and the exponent can be any number. This yields x = 5 , 2 Case 2 : x 2 − 7 x + 1 1 = − 1 and the exponent must be even. This yields x = 3
Case 3 : x 2 − 6 x − 7 = 0 This yields x = 7 , − 1
So the sum of all values of x is 5 + 2 + 3 + 7 − 1 = 1 6
Case 1: x 2 − 6 x − 7 = 0
x 2 − 6 x − 7 = 0
( x − 7 ) ( x + 1 ) = 0
x = 7 , − 1
Case 2: x 2 − 7 x + 1 1 = 1
x 2 − 7 x + 1 1 = 1
x 2 − 7 x + 1 0 = 0
( x − 5 ) ( x − 2 ) = 0
x = 5 , 2
Case 3: x 2 − 7 x + 1 1 = 1 and x 2 − 6 x − 7 = 2 k
As x 2 − 6 x − 7 = ( x − 7 ) ( x + 1 ) , ( x − 7 ) and ( x + 1 ) have the same parity ∴ x 2 − 6 x − 7 = 2 k only for odd x
x 2 − 7 x + 1 1 = − 1
x 2 − 7 x + 1 2 = 0
( x − 4 ) ( x − 3 ) = 0
Then odd x and solution of x 2 − 7 x + 1 1 = − 1 is x = 3
The sum of all values for x is 7 − 1 + 5 + 2 + 3 = 1 6
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There are three cases to check when solving this problem: when the base is equal to 1 , when the exponent is equal to 0 and the base is not equal to 0 , and when the base is equal to − 1 and the exponent is divisible by 2 .
Case 1: x 2 − 7 x + 1 1 = 1
x 2 − 7 x + 1 1 = 1
⇒ x 2 − 7 x + 1 0 = 0
⇒ ( x − 2 ) ( x − 5 ) = 0
This shows that x = 2 and x = 5 are solutions.
Case 2: x 2 − 6 x − 7 = 0
x 2 − 6 x − 7 = 0
⇒ ( x + 1 ) ( x − 7 ) = 0
Checking x = − 1 and x = 7 in the base, we find that neither of those cause the base to be equal to 0 , so x = − 1 and x = 7 can be accepted as solutions.
Case 3: x 2 − 7 x + 1 1 = − 1 , x ≡ 1 mod 2
x 2 − 7 x + 1 1 = − 1
⇒ x 2 − 7 x + 1 2 = 0
⇒ ( x − 3 ) ( x − 4 ) = 0
Checking x = 3 and x = 4 in the exponent, we find that x = 3 causes the exponent to be divisible by 2 but x = 4 does not. Thus, we can only accept x = 3 as a solution.
Our solutions are x ∈ { − 1 , 2 , 3 , 5 , 7 } . The sum of the solutions is 1 6