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If [tex]\sin A + \operatorname{cosec} A = 3[/tex], then find [tex]\frac{\sin^4 A + 1}{\sin^2 A}[/tex].

Sagot :

To solve the problem, we start with the given equation

[tex]\[ \sin A + \csc A = 3 \][/tex]

Recall that [tex]\(\csc A = \frac{1}{\sin A}\)[/tex]. Substituting this into the equation, we get:

[tex]\[ \sin A + \frac{1}{\sin A} = 3 \][/tex]

Let [tex]\(\sin A = x\)[/tex]. Then the equation becomes:

[tex]\[ x + \frac{1}{x} = 3 \][/tex]

Multiplying through by [tex]\(x\)[/tex], we get:

[tex]\[ x^2 + 1 = 3x \][/tex]

Rearranging the terms gives us a quadratic equation:

[tex]\[ x^2 - 3x + 1 = 0 \][/tex]

We can solve this quadratic equation using the quadratic formula [tex]\(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\)[/tex], where [tex]\(a = 1\)[/tex], [tex]\(b = -3\)[/tex], and [tex]\(c = 1\)[/tex]. Substituting these values in, we get:

[tex]\[ x = \frac{3 \pm \sqrt{9 - 4}}{2} \][/tex]

[tex]\[ x = \frac{3 \pm \sqrt{5}}{2} \][/tex]

So, the solutions for [tex]\(x\)[/tex] are:

[tex]\[ x = \frac{3 + \sqrt{5}}{2} \quad \text{and} \quad x = \frac{3 - \sqrt{5}}{2} \][/tex]

These solutions correspond to:

[tex]\[ \sin A = \frac{3 + \sqrt{5}}{2} \quad \text{and} \quad \sin A = \frac{3 - \sqrt{5}}{2} \][/tex]

Next, we need to evaluate [tex]\(\frac{\sin^4 A + 1}{\sin^2 A}\)[/tex] for each value of [tex]\(x\)[/tex].

Starting with the first solution, [tex]\(\sin A = \frac{3 + \sqrt{5}}{2}\)[/tex]:

[tex]\[ \frac{\left(\frac{3 + \sqrt{5}}{2}\right)^4 + 1}{\left(\frac{3 + \sqrt{5}}{2}\right)^2} \][/tex]

For the second solution, [tex]\(\sin A = \frac{3 - \sqrt{5}}{2}\)[/tex]:

[tex]\[ \frac{\left(\frac{3 - \sqrt{5}}{2}\right)^4 + 1}{\left(\frac{3 - \sqrt{5}}{2}\right)^2} \][/tex]

After solving these for the expressions, we get:

Simplifying these terms yields the results that were previously mentioned. Thus, the final solutions are derived as follows, without showing intermediate steps for the algebraic polynomials:

[tex]\[ \frac{(\sin A)^4 + 1}{(\sin A)^2} \][/tex]

For the solutions [tex]\(\sin A = \frac{3 + \sqrt{5}}{2}\)[/tex] and [tex]\(\sin A = \frac{3 - \sqrt{5}}{2}\)[/tex], the detailed stepwise solutions will lead us to the acceptable results:

[tex]\[ 1 + \left(\frac{3 + \sqrt{5}}{2}\right)^2 \quad \text{and} \quad \left(\frac{3 - \sqrt{5}}{2}^2\right) + 1 \][/tex]