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In triangle ABC, altitudes AD and BE are drawn to the corresponding bases. If ∠BAC=45∘\angle BAC = 45^\circ and ∠ABC=θ\angle ABC = \theta, then ADBE\frac{AD}{BE} equals

Solution

✅ Correct Option: 4

We have triangle ABC where ∠BAC=45°\angle BAC = 45°, ∠ABC=θ\angle ABC = θ, AD is altitude from vertex A to side BC, BE is altitude from vertex B to side AC, and we need to find ADBE\tfrac{AD}{BE}.


Both altitudes help us calculate the same area of triangle ABC, just using different base-height pairs.

Area of triangle ABC can be expressed in two ways:

Using base BC and height AD: Area =12×BC×AD= \frac{1}{2} \times BC \times AD

Using base AC and height BE: Area =12×AC×BE= \frac{1}{2} \times AC \times BE

Since both expressions equal the same area:

12×BC×AD=12×AC×BE\frac{1}{2} \times BC \times AD = \frac{1}{2} \times AC \times BE

BC×AD=AC×BEBC \times AD = AC \times BE

Therefore: ADBE=ACBC\frac{AD}{BE} = \frac{AC}{BC}


Now we need to find the ratio ACBC\tfrac{AC}{BC} using our given angles.

Law of Sines states: In any triangle, the ratio of a side to the sine of its opposite angle is constant.

For triangle ABC:

ACsin⁡(∠ABC)=BCsin⁡(∠BAC)\frac{AC}{\sin(\angle ABC)} = \frac{BC}{\sin(\angle BAC)}

ACsin⁡(θ)=BCsin⁡(45°)\frac{AC}{\sin(θ)} = \frac{BC}{\sin(45°)}

Since sin⁡(45°)=12\sin(45°) = \frac{1}{\sqrt{2}}:

ACsin⁡(θ)=BC12\frac{AC}{\sin(θ)} = \frac{BC}{\frac{1}{\sqrt{2}}}

ACBC=sin⁡(θ)sin⁡(45°)\frac{AC}{BC} = \frac{\sin(θ)}{\sin(45°)}

=sin⁡(θ)12= \frac{\sin(θ)}{\frac{1}{\sqrt{2}}}

=2sin⁡(θ)= \sqrt{2} \sin(θ)


Since ADBE=ACBC\frac{AD}{BE} = \frac{AC}{BC}, we have:

ADBE=2sin⁡(θ)\frac{AD}{BE} = \sqrt{2} \sin(θ)

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