00:02
In this question it is given that a, b, c are three distinct real numbers in gp and a plus b plus c is equal to x into b, then we have to prove that either x less than minus 1 or x greater than 3.
00:20
Given a, b, c are in gp, therefore b square is equal to a into c.
00:41
Consider this as equation.
00:43
1.
00:47
Given a plus b plus c is equal to x into b.
01:05
A plus c is equal to x into b minus b.
01:19
A plus c is equal to b b into x minus 1.
01:32
Squaring both side we get a plus c whole square is equal to a plus c whole square is equal to b square into x minus 1 whole square a square plus 2 a c plus c squared substitute b square is equal to a into c from equation 1 from equation 1 divide both side by a square a square plus 2 a c square upon a square is equal to ac upon a square into x minus one whole a square 1 plus 2 c upon a plus c upon a whole square minus c upon a into x minus 1 1 whole square is 0.
03:24
C upon a whole square plus c upon a into 2 minus x minus 1 whole square plus 1 is equal to 0.
03:45
It is a quality equation in terms of c upon a because a, b, b, c are real numbers.
04:13
So c upon a is also a real number...