cos(7π+x)=–√2/2 или cos(7π+x)=√2/2
(7π+x)= ± arccos(–√2/2)+2πk, k ∈ Z или (7π+x)= ± arccos(√2/2) +2πn, n ∈ Z
(7π+x)= ±(π – arccos(√2/2))+2πk, k ∈ Z или (7π+x)= ± (π/4) +2πn, n ∈ Z
(7π+x)= ±(π – (π/4))+2πk, k ∈ Z или (7π+x)= ± (π/4) +2πn, n ∈ Z
(7π+x)= ±(3π/4))+2πk, k ∈ Z или (7π+x)= ± (π/4) +2πn, n ∈ Z
x= ±(3π/4))–7π+2πk, k ∈ Z или x= ± (π/4)–7π +2πn, n ∈ Z