if x ^ 2 + 1 / x ^ 2 = 9 , what is the value of x ^ 4 + 1 / x ^ 4 ?
"important : i notice that if we square x ² , we get x ⁴ , and if we square 1 / x ² , we get 1 / x ⁴ , so let ' s see what happens if we take the equation x ² + 1 / x ² = 9 andsquareboth sides : ( x ² + 1 / x ² ) ² = 81 so , ( x ² + 1 / x ² ) ( x ² + 1 / x ² ) = 81 expand to get : x ⁴ + 1 + 1 + 1 / x ⁴ = 81 simplify : x ⁴ + 1 / x ⁴ = 79 answer : c"
subtract(power(2, 2), 2)