Five students are to be selected from 6 grade 9 students, 10 grade 10 students, 8 grade 11 students, and 9 grade 12 students. In how many ways could they all be from the same grade? Please show the steps. *

Use addition and subtraction to simplify the following polynomials. a. add polynomials: (3 – 4x + 8x^2) + (–6 + 2x – 5x^2) step 1: rewrite the polynomials without the parentheses. step 2: write the polynomial in descending order and use parentheses around like terms. step 3: add the like terms identified in step 2 to simplify the polynomial. b. subtract polynomials: (3x – 5 – 7x^2) – (–2 + 6x^2 – 5x) step 1: rewrite the polynomials without the parentheses. remember to multiply each term in the second parentheses by –1. show your work. step 2: write the polynomial in descending order and use parentheses around like terms. step 3: add the like terms identified in step 2 to simplify the polynomial.

What are “like terms”? why can we only add like terms?

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.