Romans 6:23 (CSB) For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.

Life * sin = death

Life * sin (confess + believe) = eternal life 

If we have sinned even once our end result is death. But thank God, He has provided a way to eternal life with Him through Jesus’ death on the cross. All we have to do confess and believe. We have to confess that Jesus is the only one to rule in our hearts and believe that Jesus is alive. 

Romans 10:9-10 (CSB) 9 If you confess with your mouth, "Jesus is Lord," and believe in your heart that God raised him from the dead, you will be saved. 10 One believes with the heart, resulting in righteousness, and one confesses with the mouth, resulting in salvation.

Eternal life is God’s gift to the one who confesses and believes because He wants to have fellowship with us. We are a creation that is very good in his sight (Genesis 1-2). But we must confess and believe because Sin does separate us from God. Jesus is the only one in whom we must confess and believe because He is the only way to eternal life with God. 

Back to the two math problems. Life with sin in it will result in death, but if we confess and believe then sin is nullified and we get eternal life. 

1 John 1:7-10 (CSB) 7 If we walk in the light as he himself is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin. 8 If we say, "We have no sin," we are deceiving ourselves, and the truth is not in us. 9 If we confess our sins, he is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness. 10 If we say, "We have not sinned," we make him a liar, and his word is not in us.