Songfacts®:

• This track from Beyoncé's fourth solo album, 4, is a piano-driven heartfelt ballad about the power of her love for her man. "I don't know much about algebra but one plus one is two," she croons, revealing she does know something about arithmetic. "He ain't got nothing but love. Darling, you got enough for the both of us. Make love when my days look low, pull me in close." The Texan songstress debuted the tune on the season 10 finale of American Idol on May 25, 2011. She introduced it as her "favorite" song, and sang it in a purple dress with red lights. The single was made available for download via the iTunes Store in the United States on the same day.
• The tune was penned by long-time collaborator The-Dream and was a contender for his third album, Love King. The R&B songwriter and producer's previous contributions to Beyoncé singles include credits for her girl-power anthems "Single Ladies (Put a Ring on It)" and "Run The World (Girls)."
• The-Dream penned this song during a time when his own marriage to singer Christina Milian was disintegrating. Speaking with UK newspaper The Guardian, the songwriter acknowledged the paradox that he is able to write so convincingly from a female perspective whilst hopeless in his own relationships with women. "I know how a woman thinks," he said, "that doesn't mean that I agree with it."
• The-Dream revealed that it was his label boss L.A. Reid who made the call not to include the track on his Love vs. Money album. "L.A. Reid said he didn't like it so we took it off," The-Dream said on the video conversation series Genius Level. "So to say '1 + 1' had been forgotten by me, that's the truth. I forgot it. I forgot it was there. It was just there on the hard drive floating there amongst the rest of the seas of songs. Because at that point it was: if I wasn't going to sing it, I wasn't going to give it to someone else because I didn't think anyone else could sing it."
  
  It was Roc Nation's Chaka Pilgrim who reminded The-Dream about the song a few years later. Pilgrim suggested that he play it for Beyoncé, and the rest is history.