How to find x in an isosceles triangle

Here we will solve some numerical problems on the properties of isosceles triangles.

1. Find x° from the below figures.

How to find x in an isosceles triangle

Solution: 

In ∆XYZ, XY = XZ.

Therefore, ∠XYZ = ∠XZY = x°.

Now, ∠YXZ + ∠XYZ + XZY = 180°

⟹ 84° + x° + x° = 180°

⟹ 2x° = 180° - 84°

⟹ 2x° = 96°

⟹ x° = 48°

2. Find x° from the given figures.

How to find x in an isosceles triangle

Solution: 

LMN, LM = MN.

Therefore, ∠MLN = ∠MNL

Thus, ∠MLN = ∠MNL = 55°, [since ∠MLN = 55°]

Now, ∠MLN + ∠LMN + ∠MNL = 180°

⟹ 55° + x° + 55° = 180°

⟹ x° + 110° = 180°

⟹ x° = 180° - 110°

⟹ x° = 70°

3. Find x° and y° from the given figure.

How to find x in an isosceles triangle

Solution:

In ∆XYP,

∠YXP = 180° - ∠QXY, as they form a linear pair.

Therefore, ∠YXP = 180° - 130°

⟹ ∠YXP = 50°

Now, XP = YP

⟹ ∠YXP = ∠XYP = 50°.

Therefore, ∠XPY = 180° - (∠YXP + ∠XYP), as the sum of three angles of a triangle is 180°

⟹ ∠XPY = 180° - (50° + 50°)

⟹ ∠XPY = 180° - 100°

⟹ ∠XPY = 80°

Now, x° = ∠XPZ = 180° - ∠XPY (linear pair).

⟹ x° = 180° - 80°

⟹ x° = 100°

Also, in ∆XPZ we have,

XP = ZP

Therefore, ∠PXZ = ∠XZP = z°

Therefore, in ∆XPZ we have,

∠XPZ + ∠PXZ + ∠XZP = 180°

⟹ x° + z° + z° = 180°

⟹ 100° + z° + z° = 180°

⟹ 100° + 2z° = 180°

⟹ 2z° = 180° - 100°

⟹ 2z° = 80°

⟹ z° = \(\frac{80°}{2}\)

⟹ z° = 40°

Therefore, y° = ∠XZR = 180° - ∠XZP

⟹ y° = 180° - 40°

⟹ y° = 140°.

4. In the adjoining figure, it is given that XY = 3y, XZ = 7x, XP = 9x and XQ = 13 + 2y. Find the values of x and y.

How to find x in an isosceles triangle

Solution:

It is given that XY = XZ

Therefore, 3y = 7x

⟹ 7x - 3y = 0 ............................ (I)

Also, we have XP = XQ

Therefore, 9x = 13 + 2y

⟹ 9x – 2y – 13 = 0 ............................ (II)

Multiplying (I) by (II), we get:

14x - 6y = 0 ............................ (III)

Multiplying (II) by (III), we get:

27x – 6y – 39 = 0 ............................ (IV)

Subtracting (III) from (IV) we get,

13x - 39 = 0

⟹ 13x = 39

⟹ x = \(\frac{39}{13}\)

⟹ x = 3

Substituting x = 3 in (I) we get,

7 × 3 – 3y = 0

⟹ 21 – 3y =0

⟹ 21 = 3y

⟹ 3y = 21

⟹ y = \(\frac{21}{3}\)

⟹ y = 7.

Therefore, x = 3 and y = 7.

9th Grade Math

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Triangle $ABC$ is isosceles with base segment $AC$. If the measure of $A = 2x+y$, the measure of $B = y$, and the measure of $C = 3x+10$, how can I find $x$ and $y$ algebraically?

When I tried to solve this problem, I made all the measures of all the angles equal to $180 (2x+y+y+3x+10=180)$, then, simplified. I used substitution to plug what $y$ equals into the same equation - but, my base angles are not congruent.

What was the error I made in my solution that was incorrect?

Isosceles triangle

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How to find x in an isosceles triangle
 
How to find x in an isosceles triangle

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How to find x in an isosceles triangle
 
How to find x in an isosceles triangle

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How do you find the X in a triangle?

Solving for X in a Right Triangle Subtract the sum of the two angles from 180 degrees. The sum of all the angles of a triangle always equals 180 degrees. Write down the difference you found when subtracting the sum of the two angles from 180 degrees. This is the value of X.

What is the formula for a isosceles triangle?

For an isosceles triangle, the area can be easily calculated if the height (i.e. the altitude) and the base are known. Multiplying the height with the base and dividing it by 2, results in the area of the isosceles triangle.

How do you find the missing value in an isosceles triangle?

The missing angle is not opposite the two marked sides and so, we add the two base angles together and then subtract this result from 180 to get our answer. The two base angles add to make 140°. Angles in an isosceles triangle add to 180°. We subtract the 140° from 180° to see what the size of the remaining angle is.