Solve the following fourth-degree equations by substituting z=x^2
a. 5x^4 - 23x^2 + 18 = 0
b. 6x^4 + 21x^2 + 12 = 10x^2 + 8
A fourth-degree equation is solved by using a substitution. The solution is detailed and well presented. The response received a rating of "5/5" from the student who originally posted the question.