Is (1-sin^4(a))/(cos^2(a))=2-cos^2(a) ?

The answer to whether (1-sin^4(a))/(cos^2(a))=2-cos^2(a) is True

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Popular Trigonometry >

prove (1-sin^4(a))/(cos^2(a))=2-cos^2(a)

Solution

prove

\frac{1 - sin ^{4} ( a )}{cos ^{2} ( a )} = 2 - cos^{2} (a)

Solution

True

Solution steps

\frac{1 - sin ^{4} ( a )}{cos ^{2} ( a )} = 2 - cos^{2} (a)

Manipulating left side

\frac{1 - sin ^{4} ( a )}{cos ^{2} ( a )}

Rewrite using trig identities

\frac{1 - sin ^{4} ( a )}{cos ^{2} ( a )}

Use the Pythagorean identity:

cos^{2} (x) + sin^{2} (x) = 1

cos^{2} (x) = 1 - sin^{2} (x)

= \frac{1 - sin ^{4} ( a )}{1 - sin ^{2} ( a )}

Simplify

\frac{1 - sin ^{4} ( a )}{1 - sin ^{2} ( a )} : sin^{2} (a) + 1

\frac{1 - sin ^{4} ( a )}{1 - sin ^{2} ( a )}

Factor

1 - sin^{4} (a) : - (sin^{2} (a) + 1) (sin (a) + 1) (sin (a) - 1)

1 - sin^{4} (a)

Factor out common term

- 1

= - (sin^{4} (a) - 1)

Factor

sin^{4} (a) - 1 : (sin^{2} (a) + 1) (sin (a) + 1) (sin (a) - 1)

sin^{4} (a) - 1

Rewrite

sin^{4} (a) - 1

(sin^{2} (a))^{2} - 1^{2}

sin^{4} (a) - 1

Rewrite

1

1^{2}

= sin^{4} (a) - 1^{2}

Apply exponent rule:

a^{b c} = (a^{b})^{c}

sin^{4} (a) = (sin^{2} (a))^{2}

= (sin^{2} (a))^{2} - 1^{2}

= (sin^{2} (a))^{2} - 1^{2}

Apply Difference of Two Squares Formula:

x^{2} - y^{2} = (x + y) (x - y)

(sin^{2} (a))^{2} - 1^{2} = (sin^{2} (a) + 1) (sin^{2} (a) - 1)

= (sin^{2} (a) + 1) (sin^{2} (a) - 1)

Factor

sin^{2} (a) - 1 : (sin (a) + 1) (sin (a) - 1)

sin^{2} (a) - 1

Rewrite

1

1^{2}

= sin^{2} (a) - 1^{2}

Apply Difference of Two Squares Formula:

x^{2} - y^{2} = (x + y) (x - y)

sin^{2} (a) - 1^{2} = (sin (a) + 1) (sin (a) - 1)

= (sin (a) + 1) (sin (a) - 1)

= (sin^{2} (a) + 1) (sin (a) + 1) (sin (a) - 1)

= - (sin^{2} (a) + 1) (sin (a) + 1) (sin (a) - 1)

= - \frac{( sin ^{2} ( a ) + 1 ) ( sin ( a ) + 1 ) ( sin ( a ) - 1 )}{1 - sin ^{2} ( a )}

Factor

1 - sin^{2} (a) : - (sin (a) + 1) (sin (a) - 1)

1 - sin^{2} (a)

Factor out common term

- 1

= - (sin^{2} (a) - 1)

Factor

sin^{2} (a) - 1 : (sin (a) + 1) (sin (a) - 1)

sin^{2} (a) - 1

Rewrite

1

1^{2}

= sin^{2} (a) - 1^{2}

Apply Difference of Two Squares Formula:

x^{2} - y^{2} = (x + y) (x - y)

sin^{2} (a) - 1^{2} = (sin (a) + 1) (sin (a) - 1)

= (sin (a) + 1) (sin (a) - 1)

= - (sin (a) + 1) (sin (a) - 1)

= \frac{( sin ^{2} ( a ) + 1 ) ( sin ( a ) + 1 ) ( sin ( a ) - 1 )}{( sin ( a ) + 1 ) ( sin ( a ) - 1 )}

Cancel

\frac{( sin ^{2} ( a ) + 1 ) ( sin ( a ) + 1 ) ( sin ( a ) - 1 )}{( sin ( a ) + 1 ) ( sin ( a ) - 1 )} : sin^{2} (a) + 1

\frac{( sin ^{2} ( a ) + 1 ) ( sin ( a ) + 1 ) ( sin ( a ) - 1 )}{( sin ( a ) + 1 ) ( sin ( a ) - 1 )}

Cancel the common factor:

sin (a) + 1

= \frac{( sin ^{2} ( a ) + 1 ) ( sin ( a ) - 1 )}{sin ( a ) - 1}

Cancel the common factor:

sin (a) - 1

= sin^{2} (a) + 1

= sin^{2} (a) + 1

= sin^{2} (a) + 1

Use the Pythagorean identity:

cos^{2} (x) + sin^{2} (x) = 1

sin^{2} (x) = 1 - cos^{2} (x)

= 1 - cos^{2} (a) + 1

Simplify

1 - cos^{2} (a) + 1 : - cos^{2} (a) + 2

1 - cos^{2} (a) + 1

Group like terms

= - cos^{2} (a) + 1 + 1

Add the numbers:

1 + 1 = 2

= - cos^{2} (a) + 2

= - cos^{2} (a) + 2

= - cos^{2} (a) + 2

= 2 - cos^{2} (a)

We showed that the two sides could take the same form

\Rightarrow True

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Is (1-sin^4(a))/(cos^2(a))=2-cos^2(a) ?
The answer to whether (1-sin^4(a))/(cos^2(a))=2-cos^2(a) is True