Find all values of satisfying\(Find all values of $x$ satisfying \[ \sqrt{4x-3}+\frac{10}{\sqrt{4x-3}}=7. \] \)
Solve sqrt(4x - 3) + 10 / sqrt(4x - 3) = 7
First note that the expression 4x - 3 is under the square root sign.
Since this value must be positive: 4x - 3 >= 0 ---> 4x >= 3 ---> x >= 4/3
To remove the denominator from the problem multiply each side by sqrt(4x - 3):
sqrt(4x - 3) [ sqrt(4x - 3) + 10 / sqrt(4x - 3) ] = sqrt(4x - 3) [ 7 ]
---> sqrt(4x - 3) · sqrt(4x - 3) + sqrt(4x - 3) · 10 sqrt(4x - 3) = 7· sqrt(4x - 3)
---> (4x - 3) + 10 = 7 · sqrt(4x - 3)
---> 4x + 7 = 7·sqrt(4x - 3)
Square both sides: [ 4x + 7 ]2 = [ 7·sqrt(4x - 3) ]2
4x2 + 56x + 49 = 49(4x - 3)
---> 4x2 + 56x + 49 = 196x - 147
Subtract 196x from both sides, add 147 to both sides:
---> 4x2 - 140x + 196 = 0
Divide both sides by 4:
---> x2 - 35x + 49 = 0
Factor: (4x - 7)(x - 7) = 0
So, either 4x - 7 = 0 ---> x = 7/4 or x - 7 = 0 ---> x = 7
Since both answers are > 4/3, these are possible answer.
I'll leave the check for you ...
Solve sqrt(4x - 3) + 10 / sqrt(4x - 3) = 7
First note that the expression 4x - 3 is under the square root sign.
Since this value must be positive: 4x - 3 >= 0 ---> 4x >= 3 ---> x >= 4/3
To remove the denominator from the problem multiply each side by sqrt(4x - 3):
sqrt(4x - 3) [ sqrt(4x - 3) + 10 / sqrt(4x - 3) ] = sqrt(4x - 3) [ 7 ]
---> sqrt(4x - 3) · sqrt(4x - 3) + sqrt(4x - 3) · 10 sqrt(4x - 3) = 7· sqrt(4x - 3)
---> (4x - 3) + 10 = 7 · sqrt(4x - 3)
---> 4x + 7 = 7·sqrt(4x - 3)
Square both sides: [ 4x + 7 ]2 = [ 7·sqrt(4x - 3) ]2
4x2 + 56x + 49 = 49(4x - 3)
---> 4x2 + 56x + 49 = 196x - 147
Subtract 196x from both sides, add 147 to both sides:
---> 4x2 - 140x + 196 = 0
Divide both sides by 4:
---> x2 - 35x + 49 = 0
Factor: (4x - 7)(x - 7) = 0
So, either 4x - 7 = 0 ---> x = 7/4 or x - 7 = 0 ---> x = 7
Since both answers are > 4/3, these are possible answer.
I'll leave the check for you ...
Let √[4x - 3] = q^2
So we have
q^2 + 10/q^2 = 7 multiply both sides by q^2
q^4 + 10 = 7q^2
q^4 - 7q^2 + 10 = 0 factor
(q^2 - 5) ( q^2 - 2) = 0
So either
q^2 = 5 or q^2 = 2 .....so....
√[4x - 3] = 5 square both sides
4x - 3 = 25 add 3 to both sides
4x = 28
x = 7
Or
√[4x - 3] = 2 square both sides
4x - 3 = 4 add 3 to both sides
4x = 7
x = 7/4
Check x = 7
√[4x - 3] + 10 / √[4x - 3] = 7 ??
√[4*7 - 3] + 10 / √[4*7 - 3] = 7 ??
5 + 10/5 = 7 is true
Check x = 7/4
√[4(7/4) - 3] + 10 / √[4(7/4) - 3] = 7 ??
√[7-3] + 10 / √[7 - 3]] = 7 ??
2 + 10/2 = 7 is also true
So x = 7 or x = 7/4