Question

Find the range of values of $x:x^2+7x\ge 30$

• A. $-3\le x\le 10$
• B. $-10\le x\le 3$
• C. $x\le -10$ or $x\ge 3$
• D. $x\le -3$ or $x\ge 10$
• E. $-11\le x\le 4$

Answer 1

The correct option is C $x\le -10$ or $x\ge 3$

• $x^2+7x\ge 30$ , which implies $x^2+7x-30\ge 0$
  
• we get $(x+10)(x-3)\ge 0$ , therefore $x\le -10$ and $x\ge 3$