x−2y+5z=0...........(i)
−2x+4y+z=0..........(ii)
−7x+14y+9z=0..........(iii)
Applying 2× equation (i)+equation (ii), we get
z=0
Putting z=0 in equation (i), we get
x=2y
Given 15≤x2+y2+z2≤150
⇒15≤4y2+y2≤150
⇒3≤y2≤30
⇒y=±2,±3,±4,±5
⇒8 solutions.
Let S be the set of all integer solutions (x,y,z) of the system of equations
x−2y+5z=0
−2x+4y+z=0
−7x+14y+9z=0
such that 15≤x2+y2+z2≤150. Then, the number of elements in the set S is equal to ..........
Held on 3 Sept 2020 · Verified 6 Jul 2026.
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