Examples with solutions for Square of sum: Using variables

Exercise #1

Consider the following relationships between the variables x and y:

x2+4=6y x^2+4=-6y

y2+9=4x y^2+9=-4x

Which answer is correct?

Video Solution

Step-by-Step Solution

To determine the correct relationship between x x and y y , let's transform each equation:

Step 1: Transform the First Equation

The first equation is x2+4=6y x^2 + 4 = -6y . Rearranging gives us:

x2=6y4 x^2 = -6y - 4

Now, aim to complete the square for expressions involving x x and y y .

Step 2: Transform the Second Equation

The second equation is y2+9=4x y^2 + 9 = -4x . Rearranging gives us:

y2=4x9 y^2 = -4x - 9

Step 3: Complete the Square

Let's complete the square for the terms x2 x^2 and y2 y^2 .

For x2=6y4 x^2 = -6y - 4 :

x2+4x+4=6y x^2 + 4x + 4 = -6y

Thus, it becomes:

(x+2)2=6y (x + 2)^2 = -6y

For y2=4x9 y^2 = -4x - 9 :

y2+6y+9=4x y^2 + 6y + 9 = -4x

Thus, it becomes:

(y+3)2=4x (y + 3)^2 = -4x

Step 4: Combine and Analyze

Substitute back to express a sum of squares:

Adding these completes the square:

(x+2)2+(y+3)2=0 (x + 2)^2 + (y + 3)^2 = 0

This result shows that both squares, squared terms are zero-sum, revealing the conditions under which equations balance.

Thus, the correct choice according to the transformations conducted is:

(x+2)2+(y+3)2=0 (x+2)^2 + (y+3)^2 = 0

Therefore, the solution to the problem is (x+2)2+(y+3)2=0 (x+2)^2 + (y+3)^2 = 0 .

Answer

(x+2)2+(y+3)2=0 (x+2)^2+(y+3)^2=0

Exercise #2

Solve the following system of equations:

{x+y=61+6xy=9 \begin{cases} \sqrt{x}+\sqrt{y}=\sqrt{\sqrt{61}+6} \\ xy=9 \end{cases}

Video Solution

Step-by-Step Solution

To solve this problem, we will follow these steps:

  • Step 1: Identify the equations and express one variable in terms of the other.
  • Step 2: Substitute into the other equation and simplify.
  • Step 3: Perform calculations to solve for the variable.
  • Step 4: Use the solution to find the second variable.

Let's work through the solution together:

Step 1: Given xy=9 xy = 9 , express y y as 9x \frac{9}{x} .

Step 2: Substitute into the first equation:

x+9x=61+6 \sqrt{x} + \sqrt{\frac{9}{x}} = \sqrt{\sqrt{61} + 6} .

Step 3: Simplify this equation. Let a=x a = \sqrt{x} and b=y b = \sqrt{y} .

Then, a+b=61+6 a + b = \sqrt{\sqrt{61} + 6} and ab=9=3 ab = \sqrt{9} = 3 .

Squaring both sides of the linear equation:

(a+b)2=61+6 (a + b)^2 = \sqrt{61} + 6 .

a2+2ab+b2=61+6 a^2 + 2ab + b^2 = \sqrt{61} + 6 .

Using ab=3 ab = 3 , we get 2ab=6 2ab = 6 .

This leads to a2+b2=61 a^2 + b^2 = \sqrt{61} .

Replacing a=x a = \sqrt{x} and b=y b = \sqrt{y} :

Let a2=x a^2 = x and b2=y b^2 = y and use the identity (ab)2=a2+b22ab=616(a - b)^2 = a^2 + b^2 - 2ab = \sqrt{61} - 6.

So, ab=616 a - b = \sqrt{\sqrt{61} - 6} .

Now let S=a+b S = a + b and P=ab P = ab from previous steps.

From S=61+6 S = \sqrt{\sqrt{61} + 6} and P=3 P = 3 , solve: t2St+P=0 t^2 - St + P = 0 .

This quadratic in t t gives solutions t=S±S24P2 t = \frac{S \pm \sqrt{S^2 - 4P}}{2} .

The quadratic roots are a=61+62±52 a = \frac{\sqrt{61} + 6}{2} \pm \frac{5}{2} and b=61+6252 b = \frac{\sqrt{61} + 6}{2} \mp \frac{5}{2} .

Thus, x=a2=(612+2.5)2 x = a^2 = (\frac{\sqrt{61}}{2} + 2.5)^2 or (6122.5)2 (\frac{\sqrt{61}}{2} - 2.5)^2 .

Similarly for y y .

Therefore, the solutions are:

x=6122.5 x = \frac{\sqrt{61}}{2} - 2.5 , y=612+2.5 y = \frac{\sqrt{61}}{2} + 2.5

or

x=612+2.5 x = \frac{\sqrt{61}}{2} + 2.5 , y=6122.5 y = \frac{\sqrt{61}}{2} - 2.5 .

Answer

x=6122.5 x=\frac{\sqrt{61}}{2}-2.5

y=612+2.5 y=\frac{\sqrt{61}}{2}+2.5

or

x=612+2.5 x=\frac{\sqrt{61}}{2}+2.5

y=6122.5 y=\frac{\sqrt{61}}{2}-2.5

Exercise #3

The rectangle ABCD is shown below.

AB = X

The ratio between AB and BC is x2 \sqrt{\frac{x}{2}} .


The length of diagonal AC is labelled m.

XXXmmmAAABBBCCCDDD

Determine the value of m:

Video Solution

Step-by-Step Solution

We know that:

ABBC=x2 \frac{AB}{BC}=\sqrt{\frac{x}{2}}

We also know that AB equals X.

First, we will substitute the given data into the formula accordingly:

xBC=x2 \frac{x}{BC}=\frac{\sqrt{x}}{\sqrt{2}}

x2=BCx x\sqrt{2}=BC\sqrt{x}

x2x=BC \frac{x\sqrt{2}}{\sqrt{x}}=BC

x×x×2x=BC \frac{\sqrt{x}\times\sqrt{x}\times\sqrt{2}}{\sqrt{x}}=BC

x×2=BC \sqrt{x}\times\sqrt{2}=BC

Now let's look at triangle ABC and use the Pythagorean theorem:

AB2+BC2=AC2 AB^2+BC^2=AC^2

We substitute in our known values:

x2+(x×2)2=m2 x^2+(\sqrt{x}\times\sqrt{2})^2=m^2

x2+x×2=m2 x^2+x\times2=m^2

Finally, we will add 1 to both sides:

x2+2x+1=m2+1 x^2+2x+1=m^2+1

(x+1)2=m2+1 (x+1)^2=m^2+1

Answer

m2+1=(x+1)2 m^2+1=(x+1)^2