Qallery
Practice free →
Home
›
CBSE Class 9
›
mathematics
›
algebraicidentities
› Find (x − 1/x)² if x + 1/x = 4:
Find (x − 1/x)² if x + 1/x = 4:
A
8
B
10
C
12
D
14
Answer & Solution
Correct answer: C. 12
(x + 1/x)² = x² + 2 + 1/x², so x² + 1/x² = 4² − 2 = 14. Then (x − 1/x)² = x² − 2 + 1/x² = 14 − 2 = 12. (Beautiful: two identities together.)
Solve this in the app — CBSE Class 9 practice & 24k+ MCQs →
Related questions
Expand (2x + 3y)²:
Is (a + b)² > a² + b² always true for non-zero a, b?
If a + b = 7 and a − b = 3, find a² − b²:
Find the value of x² + y² if x + y = 10 and xy = 21:
Factorise: 9x² − 25y²:
Compute 47 × 53 using an identity:
Compute 98² using an identity:
Use an identity to compute 102² quickly: