How do you solve 2x^2 + 7 = 3x2x2+7=3x?

2 Answers
Jul 18, 2015

This equation has no real solutions.

Explanation:

When we encounter a quadratic equation, we often want to write it in the form ax^2+bx+c=0ax2+bx+c=0. In this case this gives 2x^2-3x+7=02x23x+7=0.

Sometimes it is easy to spot solutions, for instance is we have x^2+2x+1=0x2+2x+1=0, it is easy to see that (x+1)^2=x^2+2x+1=0(x+1)2=x2+2x+1=0, so it has the solution x=-1x=1, however, in this case, this is not easy to see, so we need something called the quadratic formula.

When we again look at the general form ax^2+bx+c=0ax2+bx+c=0, we can find solutions via
x=(-bpmsqrt(b^2-4ac))/(2a)x=b±b24ac2a.
In this case we get x=(3pmsqrt((-3)^2-4*2*7))/(2*2)=(3pmsqrt(9-56))/4=3/4pm1/4sqrt(-47)x=3±(3)242722=3±9564=34±1447. Since there is no real number that satisfies this equation, because sqrt(-47) is no real number, the equation 2x^2+7=3x2x2+7=3x has no real solutions. (There are however so called complex solutions, which use a constructed number ii such that i^2=-1i2=1, but since this may be too abstract I will not go into this.)

Jul 18, 2015

Use the quadratic formula to find the complex solutions:

x = (3+-i sqrt(47))/4x=3±i474

Explanation:

First subtract 3x3x from both sides to get:

2x^2-3x+7 = 02x23x+7=0

This is in the form ax^2+bx+c = 0ax2+bx+c=0, with a=2a=2, b=-3b=3 and c=7c=7.

The discriminant Delta is given by the formula:

Delta = b^2-4ac = (-3)^2 - (4xx2xx7) = 9 - 56 = -47

Since Delta < 0 the quadratic has no solutions in real numbers. It has a pair of distinct complex solutions which are complex conjugates of one another.

x = (-b+-sqrt(Delta))/(2a) = (3+-i sqrt(47))/4