if you don't know what an oblique triangle looks like her it is on the the bottom, and it basically means a triangle that does not have any right angles.
Am going to give you clues on when to use either sine law or cosine law, When you're triangle is Non-right and contains, Angle side Angle, or side side Angle at this particular point you can use sine law.
As you can see below, there is two triangles both are oblique. the first triangle represents Side Side Angle, while the other triangle represents Angle side Angle. whenever you see these kind of triangles don't hesitate to use the sine law or else you'll be stuck.
Here is the formula of sine law (Below)
sin A/a = sin B/b = sin C/c
and if you have Side Angle Side you cannot use sine law, but you've got a another law that you can use in order to solve a triangle with a SAS, which is Cosine law. There are three versions of cosine law, each one of them starts with a different letter, which it differentiate it from each others and it's really great, because that way the formula becomes more simpler and you can solve for the Oblique triangle.
As you can see there is a triangle on top right. these type of triangles are unique, It's got a Side Angle Side, at this point you won't be able to use Sine law, because the triangle is got a SAS, so the only choice you have right now is to use Cosine law.
That's what you use in order to solve a triangle that's got SAS.
Here are the three version of cosine law:
c2=a2+b2-2abcos C
a2 = b2 + c2 – 2bc cos A
b2 = a2 + c2 – 2ac cos B.
I think it's extremely vital to learn how and when to use sine & cosine law, particularly when working with trigonometry
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