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Find the exact value of the following:

(i) [tex]\sin^2 45^{\circ} + \cos^2 60^{\circ}[/tex]

(ii) [tex]\sin \frac{\pi}{3} + \cos \frac{\pi}{6}[/tex]

(iii) [tex]\csc \frac{\pi}{6} + \sec \frac{\pi}{3}[/tex]

Show that:

[tex]\sin 60^{\circ} \cos 30^{\circ} + \cos 60^{\circ} \sin 30^{\circ} = 1[/tex]

Sagot :

Sure! Let's solve each part of the question step by step.

### Part (i)
We need to find the value of [tex]\(\sin^2 45^\circ + \cos^2 60^\circ\)[/tex].

First, let's find [tex]\(\sin 45^\circ\)[/tex] and [tex]\(\cos 60^\circ\)[/tex]:
[tex]\[ \sin 45^\circ = \frac{\sqrt{2}}{2}, \quad \cos 60^\circ = \frac{1}{2} \][/tex]

Now square these values:
[tex]\[ \sin^2 45^\circ = \left(\frac{\sqrt{2}}{2}\right)^2 = \frac{2}{4} = \frac{1}{2}, \quad \cos^2 60^\circ = \left(\frac{1}{2}\right)^2 = \frac{1}{4} \][/tex]

Add these squares together:
[tex]\[ \sin^2 45^\circ + \cos^2 60^\circ = \frac{1}{2} + \frac{1}{4} = \frac{2}{4} + \frac{1}{4} = \frac{3}{4} \][/tex]

So, the exact value of [tex]\(\sin^2 45^\circ + \cos^2 60^\circ\)[/tex] is [tex]\(\frac{3}{4}\)[/tex].

### Part (ii)
We need to find the value of [tex]\(\sin \frac{\pi}{3} + \cos \frac{\pi}{6}\)[/tex].

First, let's find [tex]\(\sin \frac{\pi}{3}\)[/tex] and [tex]\(\cos \frac{\pi}{6}\)[/tex]:
[tex]\[ \sin \frac{\pi}{3} = \frac{\sqrt{3}}{2}, \quad \cos \frac{\pi}{6} = \frac{\sqrt{3}}{2} \][/tex]

Add these values together:
[tex]\[ \sin \frac{\pi}{3} + \cos \frac{\pi}{6} = \frac{\sqrt{3}}{2} + \frac{\sqrt{3}}{2} = \frac{2\sqrt{3}}{2} = \sqrt{3} \][/tex]

So, the exact value of [tex]\(\sin \frac{\pi}{3} + \cos \frac{\pi}{6}\)[/tex] is [tex]\(\sqrt{3}\)[/tex].

### Part (iii)
We need to find the value of [tex]\(\csc \frac{\pi}{6} + \sec \frac{\pi}{3}\)[/tex].

First, let's find [tex]\(\csc \frac{\pi}{6}\)[/tex] and [tex]\(\sec \frac{\pi}{3}\)[/tex]:
[tex]\[ \csc \frac{\pi}{6} = \frac{1}{\sin \frac{\pi}{6}}, \quad \sec \frac{\pi}{3} = \frac{1}{\cos \frac{\pi}{3}} \][/tex]
[tex]\[ \sin \frac{\pi}{6} = \frac{1}{2}, \quad \cos \frac{\pi}{3} = \frac{1}{2} \][/tex]
[tex]\[ \csc \frac{\pi}{6} = \frac{1}{\frac{1}{2}} = 2, \quad \sec \frac{\pi}{3} = \frac{1}{\frac{1}{2}} = 2 \][/tex]

Add these values together:
[tex]\[ \csc \frac{\pi}{6} + \sec \frac{\pi}{3} = 2 + 2 = 4 \][/tex]

So, the exact value of [tex]\(\csc \frac{\pi}{6} + \sec \frac{\pi}{3}\)[/tex] is [tex]\(4\)[/tex].

### Proof
We need to show that [tex]\(\sin 60^\circ \cos 30^\circ + \cos 60^\circ \sin 30^\circ = 1\)[/tex].

First, let's find the values involved:
[tex]\[ \sin 60^\circ = \frac{\sqrt{3}}{2}, \quad \cos 30^\circ = \frac{\sqrt{3}}{2}, \quad \cos 60^\circ = \frac{1}{2}, \quad \sin 30^\circ = \frac{1}{2} \][/tex]

Now, use these values to calculate the expression:
[tex]\[ \sin 60^\circ \cos 30^\circ + \cos 60^\circ \sin 30^\circ = \left(\frac{\sqrt{3}}{2} \cdot \frac{\sqrt{3}}{2}\right) + \left(\frac{1}{2} \cdot \frac{1}{2}\right) \][/tex]
[tex]\[ = \frac{3}{4} + \frac{1}{4} = \frac{4}{4} = 1 \][/tex]

Thus, [tex]\(\sin 60^\circ \cos 30^\circ + \cos 60^\circ \sin 30^\circ = 1\)[/tex] is indeed true.

So, we've verified this identity successfully.