Q. What is Right Angled Isoquant?

This presumes zero substitutability of factors of production. There is just one method of producing any one commodity. In this case, isoquant takes the form of a right angle as in Figure below. 

Right Angled Isoquant

In this case, capital and labour are perfect complements, which is, capital and labour should be used in fixed proportion demonstrated by point C. The output can be increased only by increasing both the quantity of capital and labour in the same proportion depicted at the point C.

This isoquant is known as input-output isoquant or Leontief isoquant after Leontief, who invented input-output analysis.