# Thread: Having trouble understanding this example

1. ## Having trouble understanding this example

Hi my maths text book has a question that says:

Solve $\displaystyle sin^2\theta$ for $\displaystyle -180\leq \theta \leq180$

and the example shows these first few lines of working:

$\displaystyle sin^2\theta=\frac{1}{2}$
$\displaystyle sin\theta = \pm\sqrt{\frac{1}{2}}$
$\displaystyle sin\theta =\pm\frac{1}{\sqrt{2}}$

but what iam wandering is what about the theta (angle) if you square root one side wouldn't you need to square root the theta as well not just the $\displaystyle sin^2$

and wouldn't the second line look like this
$\displaystyle sin\sqrt{\theta}=\pm\sqrt{\frac{1}{2}}$

2. Originally Posted by silverbird
Hi my maths text book has a question that says:

Solve $\displaystyle sin^2\theta$ for $\displaystyle -180\leq \theta \leq180$

and the example shows these first few lines of working:

$\displaystyle sin^2\theta=\frac{1}{2}$
$\displaystyle sin\theta = \pm\sqrt{\frac{1}{2}}$
$\displaystyle sin\theta =\pm\frac{1}{\sqrt{2}}$

but what iam wandering is what about the theta (angle) if you square root one side wouldn't you need to square root the theta as well not just the $\displaystyle sin^2$

and wouldn't the second line look like this
$\displaystyle sin\sqrt{\theta}=\pm\sqrt{\frac{1}{2}}$

This is because,

$\displaystyle (\sin \theta)^2$ is written as $\displaystyle \sin^2 \theta$

Also $\displaystyle \sin$ and $\displaystyle \theta$ are not separate. This whole $\displaystyle \sin \theta$ is one term.

3. that would explain it i had a feeling that might of been it. thx for your help

4. Are you sure they are not separate i was just thinking what about if you have say $\displaystyle sin\theta=50$ then to find $\displaystyle \theta$ dont you divide it by sin or multiply it by $\displaystyle sin^{-1}$ making $\displaystyle \theta$ separate ?

5. Originally Posted by silverbird
Are you sure they are not separate i was just thinking what about if you have say $\displaystyle sin\theta=50$ then to find $\displaystyle \theta$ dont you divide it by sin or multiply it by $\displaystyle sin^{-1}$ making $\displaystyle \theta$ separate ?
1. $\displaystyle sin\theta=50$ is impossible for real values of $\displaystyle \theta$.

2. If I said that $\displaystyle \sqrt{x} = 2$ would you attempt to solve this by dividing both sides by $\displaystyle \sqrt{} ?$

3. If you have $\displaystyle \sin \theta = \frac{1}{\sqrt{2}}$ then one of the solutions is $\displaystyle \theta = \sin^{-1} \frac{1}{\sqrt{2}}$. (But don't even think of worrying about where the other solutions come from until you understand the basic concepts in this post). $\displaystyle \sin^{-1}$ is an operator and ACTS on the number $\displaystyle \frac{1}{\sqrt{2}}$. It DOES NOT multiply the number.

4. Things like $\displaystyle \sqrt{}, ~ \sin, ~ \sin^{-1}$ are operators NOT numbers. They ACT on numbers. They are NOT treated like numbers.

6. 1. is impossible for real values of .
sorry about that i was rushing and didn't think. I meant something like $\displaystyle sin\theta=\frac{1}{2}$

is an operator and ACTS on the number . It DOES NOT multiply the number.
Know everything makes sense i fully understand know. Its kind of weird how they use $\displaystyle sin^2\theta$ instead of $\displaystyle (sin\theta)^2$

Anyway i cant imagine how long it took you to right all that, thank you very much you explained everything great and you have given me a better understanding of maths (because i never thought of operators before).

thank you mr fantastic