Help, please I'm working on over dues and I don't understand this

Find the area of the triangle shown 3 by 6

1c) the number 131 is a term in the sequence defined by the explicit rule f(n)=5n-4. which term in the sequence is 131? 2a) write the first four terms of the function f(n)=n^2-1 2b) what is the 10th term of the sequence defined by the explicit rule f(n)=n^2-1 2c) the number 224 is a term in the sequence defined by the explicit rule f(n)=n^2-1. which term in the sequence is 224?

In δabc, m∠acb = 90°, cd ⊥ ab and m∠acd = 45°. find: a find cd, if bc = 3 in