Question

Sin78 cos18-cos78 sin18

Answer 1

Given Equation is in the form of sin A cos B - cos A sin B.

We Know that sin A cos B - cos A sin B = sin (A - B).

Here A = 78, b = 18.

Therefore sin 78 cos 18 - cos 78 sin 18 = sin(78 - 18)

                                                                 = sin 60.

                                                                 =  root 3/2.

Hope this helps!

Answer 2

$sin78cos18-cos78sin18 = \frac{\sqrt{3} }{2} .$

• Sine and cosine are trigonometric functions of an angle in mathematics. In the context of a right triangle, the sine and cosine of an acute angle are defined as the ratio of the length of the side directly opposite the angle to the length of the longest side of the triangle (the hypotenuse), and the neighbouring leg's length to the hypotenuse, respectively.
• The definitions of sine and cosine can be expanded more broadly to include any real value in terms of the lengths of certain line segments in a unit circle.
• The sine and cosine can be extended to arbitrary positive and negative values as well as complex numbers according to more recent definitions that represent them as infinite series or as the solutions to certain differential equations.

Here, according to the given information, we are given that,

$sin78cos18-cos78sin18.$

Now, we know that,

$sin(A-B) =sinAcosB-cosAsinB.$

Now, applying this, we get,

$sin78cos18-cos78sin18\\=sin(78-18)\\=sin60\\=\frac{\sqrt{3} }{2} .$

Hence, $sin78cos18-cos78sin18 = \frac{\sqrt{3} }{2} .$

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