Question

if trigonometry is based on right angle, how can we sensibly consider, trigonometry ratios of angle greater than right angle?

Answer 1

Trigonometry is based on right angles,for beginners to grasp the concept of the side ratios.Ultimately all Trigonometry is just a bunch of ratios for different angles .If you consider a circle with radius 1,and choose any point on it ,drop a perpendicular on the horizontal diameter of the circle from that point and also join it to the center of the circle you'll land up with a right angled triangles.
Although all of its angles will be below 90,if you define the angle itself as being taken in the anticlockwise direction,starting from the x axis you'll be able to define these ratios for angles bigger than 90 also.
Honestly I'll recommend you to read some textbooks on these and search for animated videos on YouTube which explain it quite easily using graphics.
It's too difficult for me to write everything down,though I'll encourage you to draw the circle I've written about and define the angle and sides accordingly.

Answer 2

We can use the trigonometry in the negative form (90° to 180°) and (180° to 360°) we can use the addition method (eg-270° = x+y)

Hope it helps you.

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