KVPY2016MathematicsBasics of Mathematics
Consider a cuboid all of whose edges are integers and whose base is square. Suppose the sum of all its edges is numerically equal to the sum of the areas of all its six faces. Then the sum of all its edges is.
Options
- A12
- B18
- C24
- D36
Correct answer
C. 24
Step-by-step solution
Let sides are a , a , h array l So, 4 a+4 h+4 a=2 (a²+a h+a h ) 2 a+2 h+2 a=a²+2 a h a²-4 a=2 h(1-a) (a²-1 )+1-4(a-1)-4=2 h(1-a) (a-1)(a+1)-4(a-1)-3=2 h(1-a) 2 h= 3 a-1 +4-(a+1) array So a=2 & h=2 are the only integral solution (a & h are positive integers)