Suppose someone tells you that she has a triangle with sides having lengths 2.6, 8.1, and 8.6. is this a right triangle? why or why not? is there an angle in the triangle larger than 90 degree?

First you check for Pythagoras'  Theorem.

Is  8.6² = 8.1²  + 2.6²  ? 
  
8.1²  + 2.6² = 65.61 + 6.76 = 72.37
8.6² =  73.96

8.1²  + 2.6²  ≠ 8.6² 

Since Pythagoras' Theorem is not satisfied it is not a right angled triangle.

The longest side is 8.6,  let's find the angle facing the longest side 8.6.

By cosine formula  CosA =  (b² + c² - a²) / (2bc)

CosA =  (2.6² + 8.1² - 8.6²) / (2*2.6*8.1) = -1.59/42.12 = -0.0377

A = Cos inverse (-0.0377) = 92.1 degrees

So there is  an angle is greater than 90 degrees.

The answer for this is 9/1253decimal form 0.007

i = 2 / - 5

step-by-step explanation:

evaluation of ( 2 - 4 ) ( p + q ) when p = 2 and q = 5 i, by putting values of p and q,                                                                    

0 = ( 2 - 4 ) ( p + q )0 = ( 2 - 4 ) ( 2 + 5 i ),   by multiplying these0 = ( 4 + 10 i - 8 - 20 i )0 = 4 - 8 + 10 i - 20 i0 = - 4 -10 i   0 = 2 ( - 2 - 5 i )0 / 2 = - 2 - 5 i- 2 - 5 i = 0- 5 i = 2i = 2 / - 5