alleryIf a is positive and a² + 1/a² = 7, then a³ + 1/a³ equals:
A21
B3√7
C18
D7√7
Answer & Solution
Correct answer: C. 18
1. (a + 1/a)² = a² + 1/a² + 2 = 7 + 2 = 9, so a + 1/a = 3.
2. a³ + 1/a³ = (a + 1/a)³ − 3(a + 1/a).
3. = 27 − 9 = 18.
_Source: RRB Group D CEN-02/2018 PYQ, Q.39._
Keep practising Polynomials and Algebraic Identities
Browse all Polynomials and Algebraic Identities questions for CBSE Class 9, or explore more Mathematics topics.
Related questions
What is the slope of the line 2x + 3y = 6?What is the equation of the x-axis?Which of these equations is NOT a linear equation in two variables?At which point does the line x + y = 7 cut the x-axis?If x = 2 and y = k satisfy the equation 5x - 3y = 1, what is the value of k?Which ordered pair is a solution of the equation 3x + 2y = 12?Match the degree to the nameIf x and x + 10 add to 64, the linear equation is: