Question
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Catcolate the value of \( \sin 50^{\circ}+\cos 50^{\circ} \tan 20^{\circ} \) without the use of a calculator.

Ask by Paul Little. in South Africa
Feb 20,2025

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Tutor-Verified Answer

Answer

The value of \( \sin 50^{\circ} + \cos 50^{\circ} \tan 20^{\circ} \) is 1.

Solution

We start with the expression:   sin 50° + cos 50° · tan 20°. Step 1. Write tan 20° as sin 20°/cos 20°:   sin 50° + cos 50° · (sin 20°/cos 20°). Step 2. Combine the terms over a common denominator:   = (sin 50°·cos 20° + cos 50°·sin 20°) / cos 20°. Step 3. Recognize the sine angle-addition formula for the numerator:   sin 50°·cos 20° + cos 50°·sin 20° = sin (50° + 20°) = sin 70°. Thus, the expression simplifies to:   = sin 70° / cos 20°. Step 4. Notice that sin 70° is the same as cos 20° because sin 70° = cos (90° – 70°) = cos 20°. So the expression becomes:   = cos 20° / cos 20° = 1. Therefore, the value of the given expression is 1.

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To solve for \( \sin 50^{\circ}+\cos 50^{\circ} \tan 20^{\circ} \), we start by noting the trigonometric identity for tangent: \[ \tan 20^{\circ} = \frac{\sin 20^{\circ}}{\cos 20^{\circ}}. \] Substituting this into our expression gives: \[ \sin 50^{\circ} + \cos 50^{\circ} \cdot \frac{\sin 20^{\circ}}{\cos 20^{\circ}} = \sin 50^{\circ} + \frac{\cos 50^{\circ} \sin 20^{\circ}}{\cos 20^{\circ}}. \] Next, we use the co-function identity \( \sin(90^\circ - x) = \cos x \) to find that \( \sin 50^{\circ} = \cos 40^{\circ} \). Thus, the expression becomes: \[ \cos 40^{\circ} + \frac{\cos 50^{\circ} \sin 20^{\circ}}{\cos 20^{\circ}}. \] However, it is more convenient to manipulate the components: Noting that \( \cos 50^{\circ} = \sin 40^{\circ} \), we can also rewrite the second term: \[ \sin 40^{\circ} \cdot \tan 20^{\circ} = \sin 40^{\circ} \cdot \frac{\sin 20^{\circ}}{\cos 20^{\circ}}. \] Based on the identity \( \sin a \cdot \tan b = \frac{\sin a \cdot \sin b}{\cos b} \), we write: \[ \sin 40^{\circ} \cdot \tan 20^{\circ} = \frac{\sin 40^{\circ} \cdot \sin 20^{\circ}}{\cos 20^{\circ}}. \] For \( \sin 40^{\circ} = 2 \sin 20^{\circ} \cos 20^{\circ} \), this simplifies our function further: Combining these gives: \[ \sin 50^{\circ} + \cos 50^{\circ} \tan 20^{\circ} = \sin 50^{\circ} + \sin 40^{\circ} = \sin 50^{\circ} + 2\sin 20^{\circ} \cos 20^{\circ} / \cos 20^{\circ} = 1. \] Thus: \[ \sin 50^{\circ} + \cos 50^{\circ} \tan 20^{\circ} = 1. \] Therefore, the answer is \( \boxed{1} \).

Related Questions

8. Simplify without using a calculator. (8.1) \( \frac{\sin \left(180^{\circ}-x\right) \cdot \tan \left(360^{\circ}-x\right)}{\cos \left(80^{\circ}-x\right)} \times \frac{\cos \left(-180^{\circ}-x\right)}{\cos \left(360^{\circ}+x\right) \sin \left(360^{\circ}-x\right)} \) \( 8.2 \frac{\cos 135^{\circ} \sin 160^{\circ}}{\sin 225^{\circ} \cos 70^{\circ}} \) (8.3) \( \frac{\sin (-\theta)+\cos 120^{\circ}+\tan \left(-180^{\circ}-\theta\right)}{\sin ^{2} 225^{\circ}-\tan (-\theta)-\cos \left(90^{\circ}+\theta\right)} \) B.4 \( 4^{x} \frac{\sin 247^{\circ} \cdot \tan 23^{\circ} \cdot \cos 113^{\circ}}{\sin \left(-157^{\circ}\right)} \) (8.5) \( \frac{3 \cos 150^{\circ} \cdot \sin 270^{\circ}}{\tan \left(-45^{\circ}\right) \cdot \cos 600^{\circ}} \) 8.6) \( \frac{\tan \left(180^{\circ}-x\right) \cdot \sin \left(90^{\circ}+x\right)}{\sin (-x)}-\sin y \cdot \cos \left(90^{\circ}-y\right) \) \( 8.7 \frac{\tan 30^{\circ} \cdot \sin 60^{\circ} \cdot \cos 25^{\circ}}{\cos 135^{\circ} \cdot \sin \left(-45^{\circ}\right) \cdot \sin 65^{\circ}} \) 6.8) \( \frac{\tan \left(180^{\circ}-x\right) \cdot \sin \left(90^{\circ}-x\right)}{\cos \left(90^{\circ}+x\right)}-\frac{\cos \left(180^{\circ}-x\right)}{\sin \left(90^{\circ}+x\right)} \) \( 8.9 \frac{\sin 189^{\circ}}{\tan 549^{\circ}}-\frac{\cos ^{2}\left(-9^{\circ}\right)}{\sin 99^{\circ}} \) Solving trigonometric equations (no calculators) (1.) If \( \sin \mathrm{A}=\frac{-3}{5} \) and \( 0^{\circ}<\mathrm{A}<270^{\circ} \) determine the value of: \( 1.1 \cos A \) \( 1.2 \tan A \). (2.) If \( -5 \tan \theta-3=0 \) and \( \sin \theta<0 \), determine: \( 2.1 \sin ^{2} \theta^{\circ} \) \( 2.25 \cos \theta \) \( 2.3 \quad 1-\cos ^{2} \theta \) 3. If \( 13 \cos \theta+12=0 \) and \( 180^{\circ}<\theta<360^{\circ} \), evaluate: \( 3.2 \tan \theta \) \( 3.1 \sin \theta \cos \theta \) \( 3.3 \sin ^{2} \theta+\cos ^{2} \theta \). (4.) If \( 3 \tan \theta-2=0 \) and \( \theta \in\left[90^{\circ} ; 360^{\circ}\right] \), determine, the value of \( \sqrt{13}(\sin \theta-\cos \theta \) (5.) If \( \cos 52^{\circ}=k \) as illustrated in the diagram, determine each of the following i
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