If f:[−2,2]→R is defined byf(x)=⎧⎪ ⎪ ⎪⎨⎪ ⎪ ⎪⎩√1+cx−√1−cxx,for−2≤x<0x+3x+1,for0≤x≤2 is continuous on [−2,2] then c=