jawab benar dan tepat pki jln ya...

a.(5+√7)(5-√7)
25-5√7+5√7-√49
25-7
=18

b.(9-√61)(9+√61)
81+9√61-9√61-√3721
81-61
=20

c.(√23-√12)(√23+√12)
√23×√23+√23×√12-√12×√23-√12×√12
√529+√276-√276-√144
23-12
=11

Yg d krng tau, maaf yaa klo salah