-
If x² + 1 = 98(x > 0), then the value of 
x³ + 1 
is 2 x³
-
- 970
- 1030
- –970
- –1030
Correct Option: A
| x² + | = 98 | |
| x² |
| ⇒ | | x + | | ² | - 2 = 98 | |
| x |
| ⇒ | | x + | | ² | = 98 + 2 = 100 | |
| x |
| ⇒ x + | = √100 = 10.......(i) | |
| x |
On cubing both sides,
| x + | | ³ | = (10)³ = 1000 | |
| x |
| ⇒ x³ + | + 3 | | x + | | = 1000 | ||
| x³ | x |
| ⇒ x³ + | + 3 × 10 = 1000 | |
| x³ |
| ⇒ x³ + | = 1000 - 30 = 970 | |
| x³ |
