Let's denote the number as x.

According to the problem, we have the equation:

x - 4 = 21 * (1/x)

To solve this equation, we can first multiply both sides by x to get rid of the fraction:

x^2 - 4x = 21

Then, we can rearrange the equation to a standard quadratic form:

x^2 - 4x - 21 = 0

This is a quadratic equation in the form of ax^2 + bx + c = 0, where a = 1, b = -4, and c = -21.

We can solve this equation using the quadratic formula: x = [-b ± sqrt(b^2 - 4ac)] / (2a)

Substituting the values of a, b, and c into the formula, we get:

x = [4 ± sqrt((-4)^2 - 4*1*(-21))] / (2*1)
x = [4 ± sqrt(16 + 84)] / 2
x = [4 ± sqrt(100)] / 2
x = [4 ± 10] / 2

This gives us two possible solutions: x = 7 and x = -3.

However, the problem specifies that the number is positive, so the correct answer is 7.

Question

Let's denote the number as x.

According to the problem, we have the equation:

x - 4 = 21 * (1/x)

To solve this equation, we can first multiply both sides by x to get rid of the fraction:

x^2 - 4x = 21

Then, we can rearrange the equation to a standard quadratic form:

x^2 - 4x - 21 = 0

This is a quadratic equation in the form of ax^2 + bx + c = 0, where a = 1, b = -4, and c = -21.

We can solve this equation using the quadratic formula: x = [-b ± sqrt(b^2 - 4ac)] / (2a)

Substituting the values of a, b, and c into the formula, we get:

x = [4 ± sqrt((-4)^2 - 4*1*(-21))] / (2*1)
x = [4 ± sqrt(16 + 84)] / 2
x = [4 ± sqrt(100)] / 2
x = [4 ± 10] / 2

This gives us two possible solutions: x = 7 and x = -3.

However, the problem specifies that the number is positive, so the correct answer is 7.

Knowee AI · Accepted Answer