Question

can the sides of a triangle be 3, 9 and 10

Answer 1

yes they can because the two shortest sides of the triangle added together must always equal a length longer than the longest side 

Answer 2

Yes. 3+9=12 10+9=18 3+10=13. Which ever values are on the sides of a triangle, the sum of those two values has to be greater than the third value.