iMac

Please help. my spec: i5-4590 (stock cooler) gtx 750 ti 8gb My i5 4590 idle mode 45 to 50 degree. and while i'm playing games like GTA 5. my temperature Reach 75 to 81 Core 1 : 81 degree core 2 : 79 degree core 3 : 76 degree core 4 : 79 degree is this normal? :( i'm afraid using it.