Question

If xy = 10 then minimum value of 12x² + 13y² is equal to

• A. 15
• B. 40$\sqrt { 39 }$
• C. 3 $\sqrt { 13 }$
• D. 30$\sqrt { 13 }$

Answer 1

Answer: (B)

40$\sqrt { 39 }$

Answer 2

12x² + 13y² ≥ $2 \sqrt { 12.13 x ^ { 2 } y ^ { 2 } }$

= $4 \sqrt { 39 }$ |xy| = $40 \sqrt { 39 }$