find the foci of 9x^2-25y^2=225 I get this far a^2=5 and B^2=3 AND I KNOW I HAVE TO USE THE formula c^2=a^2-b^2 i don't know what to do now if add it i get c^2=34 please help show the step thanks

Question

find the foci of 9x^2-25y^2=225 I get this far a^2=5 and B^2=3  AND I KNOW I HAVE TO USE THE formula  c^2=a^2-b^2 i don't know what to do now if add it i get c^2=34 please help show the step thanks

Reiny · Answer

9x^2 - 25y^2 = 225 divide by 225 x^2/25 - y^2/9 = 1 a^2= 25 , and b^2 = 9 , (you had a^2 = 5 and b^2 = 3) ok, so c^2 = a^2 - b^2 = 25 - 9 = 34 c = ± √34 the foci are (√34,0) and (-√34 , 0)