If one of the lines 4x2−cxy+y2=0 is x+y=0 then c=

If m1,m2 are slopes of lines represented by the combined equation  ax2+2hxy+by2=0 then the equation whose roots are m1,m2 is bm2+2hm+a=0  The slope of the line x+y=0 is−1Hence -1 is the root of  m2−cm+4=0It implies that 1+c+4=0⇒c=−5