# Which pair of angles has congruent values for the sinx° and the cosy°?

Part(a) $35^{\circ};55^{\circ}$

Part(b) $35^{\circ};145^{\circ}$

Part(c) $35^{\circ};70^{\circ}$

Part(d) $35^{\circ};35^{\circ}$

This question aims to find the pair of angles concurrent to the sin x and cos y.

Congruent angles are the angles that have the same measure. So all angles that have the same size will be called congruent angles. They are seen everywhere, such as in equilateral triangles, isosceles triangles, or when a transversal intersects two parallel lines.

Angle less than degree

In mathematics, angles that are equal in the measure are known as congruent angles. In other words, equal angles are also congruent angles denoted by the $≅$. They don’t point to the same direction. They don’t have to be on lines of similar size.

Congruent Angle theorem

There are number of  theorems based on congruent angles.

1. Vertical angles theorem
2. Corresponding angles theorem
3. Alternate angles theorem
4. Congruent supplements theorem
5. Congruent complements theorem

Congruent angles

Vertical angles theorem

According to the vertical angle theorem, vertical angles are always congruent.

Corresponding angles theorem

The corresponding definition of angles tells us that when two parallel line intersected to a third, the angles that have the same relative position at each point of intersection are known as corresponding angles.

Alternate angles theorem

When a transversal intersects with the two parallel lines, each pair of alternate angles is congruent.

Congruent supplements theorem

Supplementary angles are those whose sum is $180^{\circ}$. This theorem states that angles supplementing the same angle are congruent angles, whether adjacent angles or not.

Congruent complements theorem

Supplementary angles are those whose sum is $90^{\circ}$. This theorem states that angles that supplement the same angle are congruent, whether adjacent or not.

Tips and tricks

1. Congruent angles are just another name for equal angles.
2. All vertically opposite angles are congruent angles.
3. All alternate and corresponding angles formed by the intersection of two parallel lines and a transversal are congruent.
4. According to the definition of congruent angles, “For any two angles to be congruent, they must have the same size.”

## Expert Answer

Step 1

$\cos(90-\theta)=\cos(90)\cos(\theta)+\sin(90)\sin(0)$

$\cos(90-\theta)=\sin(\theta)$

Step 2

Using $\theta=35$ then,

$\cos(90-35)=\sin(35)$

$\cos(55)=\sin(35)$

$35^{\circ},55^{\circ}$

Option $a$ is correct. $35^{\circ}$ and $55^{\circ}$ are the congruent angles to $\cos^{\circ}$ and $\sin^{\circ}$.

Vertical angle theorem

## Numerical Result

Option $a$ is correct. $35^{\circ}$ and $55^{\circ}$ are the congruent angles to $\cos^{\circ}$ and $\sin^{\circ}$.

## Example

Which pair of angles have congruent values for the $\sin⁡ x^{\circ}$ and the $\cos⁡ y^{\circ}$?

(a) $42^{\circ};42^{\circ}$

(b) $42^{\circ};48^{\circ}$

(c) $42^{\circ};138^{\circ}$

(d) $42^{\circ};132^{\circ}$

Solution

$\sin x=cos(90-x)$

$\sin(42)=cos(90-42)$

$sin(42)=cos(48)$

Option $b$ is correct.

$42^{\circ}$ and $48^{\circ}$ are the congruent angles to $\cos^{\circ}$ and $\sin^{\circ}$.

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